1、最新完整托福模拟题阅读最新完整托福模拟题阅读(一)欧阳光明（2021.03.07）Questions 12-20 The elements other than hydrogen and helium exist In such small quantities that it is accurate to say that the universe somewhat more than 25 percent helium by weight and somewhat less than 25 percent hydrogen. Astronomers hQuestions 12-20The
2、elements other than hydrogen and helium exist In such small quantities that it is accurate to say that the universe somewhat more than 25 percent helium by weight and somewhat less than 25 percent hydrogen.Astronomers have measured the abundance of helium throughout our galaxy and in other galaxies
3、as well. Helium has been found In old stars, in relatively young ones, in interstellar gas, and in the distant objects known as quasars. Helium nuclei have also been found to be constituents of cosmic rays that fall on the earth (cosmic rays are not really a form of radiation; they consist of rapidl
4、y moving particles of numerous different kinds). It doesnt seem to make very much difference where the helium is found. Its relative abundance never seems to vary much. In some places, there may be slightly more of it; In others, slightly less, but the ratio of helium to hydrogen nuclei always remai
5、ns about the same.Helium is created in stars. In fact, nuclear reactions that convert hydrogen to helium are responsible for most of the energy that stars produce. However, the amount of helium that could have been produced in this manner can be calculated, and it turns out to be no more than a few
6、percent. The universe has not existed long enough for this figure to he significantly greater. Consequently, if the universe is somewhat more than 25 percent helium now, then it must have been about 25 percent helium at a time near the beginning.However, when the universe was less than one minute ol
7、d, no helium could have existed. Calculations indicate that before this time temperatures were too high and particles of matter were moving around much too rapidly. It was only after the one-minute point that helium could exist. By this time, the universe had cooled sufficiently that neutrons and pr
8、otons could stick together. But the nuclear reactions that led to the formation of helium went on for only a relatively short time. By the time the universe was a few minutes old, helium production had effectively ceased.12. what does the passage mainly explain?(A)How stars produce energy(B)The diff
9、erence between helium and hydrogen(C)When most of the helium in the universe was formed(D)Why hydrogen is abundant13. According to the passage, helium is(A) the second-most abundant element in the universe(B) difficult to detect(C) the oldest element in the universe(D) the most prevalent element in
10、quasars14. The word constituents in line 7 is closest in meaning to(A) relatives(B) causes(C)components(D) targets15. Why does the author mention cosmic rayst in line 7?(A)As part of a list of things containing helium(B) As an example of an unsolved astronomical puzzle(C) To explain how the universe
11、 began(D) To explain the abundance of hydrogen in the universe16. The word vary in line 10 is closest ill meaning to(A) mean(B) stretch(C) change(D) include17. The creation of helium within stars(A) cannot be measured(B) produces energy(C) produces hydrogen as a by-product(D) causes helium to be muc
12、h more abundant In old stars than In young star:18. The word calculated in line 15 is closest in meaning to(A) ignored(B) converted(C) increased(D) determined19. Most of the helium in the universe was formed(A) in interstellar space(B) in a very short time(C) during the first minute of the universes
13、 existence(D) before most of the hydrogen20. The word ceased in line 26 is closest in meaning to(A)extended(B)performed(C)taken hold(D)stoppedHormones in the BodyUp to the beginning of the twentieth century, the nervous system was thought to control all communication within the body and the resultin
14、g integration of behavior. Scientists had determined that nerves ran, essentially, on electrical impulses. These impulses were thought to be the engine for thought, emotion, movement, and internal processes such as digestion. However, experiments by William Bayliss and Ernest Starling on the chemica
15、l secretin, which is produced in the small intestine when food enters the stomach, eventually challenged that view. From the small intestine, secretin travels through the bloodstream to the pancreas. There, it stimulates the release of digestive chemicals. In this fashion, the intestinal cells that
16、produce secretin ultimately regulate the production of different chemicals in a different organ, the pancreas.Such a coordination of processes had been thought to require control by the nervous system; Bayliss and Starling showed that it could occur through chemicals alone. This discovery spurred St
17、arling to coin the term hormone to refer to secretin, taking it from the Greek word hormon, meaning “to excite” or “to set in motion.” A hormone is a chemical produced by one tissue to make things happen elsewhere.As more hormones were discovered, they were categorized, primarily according to the pr
18、ocess by which they operated on the body. Some glands (which make up the endocrine system) secrete hormones directly into the bloodstream. Such glands include the thyroid and the pituitary. The exocrine system consists of organs and glands that produce substances that are used outside the bloodstrea
19、m, primarily for digestion. The pancreas is one such organ, although it secretes some chemicals into the blood and thus is also part of the endocrine system.Much has been learned about hormones since their discovery. Some play such key roles in regulating bodily processes or behavior that their abse
20、nce would cause immediate death. The most abundant hormones have effects that are less obviously urgent but can be more far-reaching and difficult to track: They modify moods and affect human behavior, even some behavior we normally think of as voluntary. Hormonal systems are very intricate. Even mi
21、nute amounts of the right chemicals can suppress appetite, calm aggression, and change the attitude of a parent toward a child. Certain hormones accelerate the development of the body, regulating growth and form; others may even define an individuals personality characteristics. The quantities and p
22、roportions of hormones produced change with age, so scientists have given a great deal of study to shifts in the endocrine system over time in the hopes of alleviating ailments associated with aging.In fact, some hormone therapies are already very common. A combination of estrogen and progesterone h
23、as been prescribed for decades to women who want to reduce mood swings, sudden changes in body temperature, and other discomforts caused by lower natural levels of those hormones as they enter middle age. Known as hormone replacement therapy (HRT), the treatment was also believed to prevent weakenin
24、g of the bones. At least one study has linked HRT with a heightened risk of heart disease and certain types of cancer. HRT may also increase the likelihood that blood clotsdangerous because they could travel through the bloodstream and block major blood vesselswill form. Some proponents of HRT have
25、tempered their enthusiasm in the face of this new evidence, recommending it only to patients whose symptoms interfere with their abilities to live normal lives.Human growth hormone may also be given to patients who are secreting abnormally low amounts on their own. Because of the complicated effects
26、 growth hormone has on the body, such treatments are generally restricted to children who would be pathologically small in stature without it. Growth hormone affects not just physical size but also the digestion of food and the aging process. Researchers and family physicians tend to agree that it i
27、s foolhardy to dispense it in cases in which the risks are not clearly outweighed by the benefits.27. The word engine in the passage is closest in meaning to(A) desire(B) origin(C) science(D) chemical28. The word it in the passage refers to(A) secretin(B) small intestine(C) bloodstream(D) pancreas29
28、. The word spurred in the passage is closest in meaning to(A) remembered(B) surprised(C) invented(D) motivated30. To be considered a hormone, a chemical produced in the body must(A) be part of the digestive process(B) influence the operations of the nervous system(C) affect processes in a different
29、part of the body(D) regulate attitudes and behavior31. The glands and organs mentioned in paragraph 3 are categorized according to(A) whether scientists understand their function(B) how frequently they release hormones into the body(C) whether the hormones they secrete influence the aging process(D)
30、 whether they secrete chemicals into the bloodParagraph 3 is marked with an arrow 32. The word key in the passage is closest in meaning to(A) misunderstood(B) precise(C) significant(D) simple33. The word minute in the passage is closest in meaning to(A) sudden(B) small(C) changing(D) noticeable34. W
31、hich of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect answer choices change the meaning in important ways or leave out essential information.(A) Most moods and actions are not voluntary because they are actually produced by the pro
32、duction of hormones in the body.(B) Because the effects of hormones are difficult to measure, scientists remain unsure how far-reaching their effects on moods and actions are.(C) When the body is not producing enough hormones, urgent treatment may be necessary to avoid psychological damage.(D) The influence of many hormones is not easy to
