Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correct answer to each of the questions.
The elements other than hydrogen and helium exist in such small quantities that it is accurate to say that the universe is somewhat more than 25 percent helium by weight and somewhat less than 75 percent hydrogen.
Astronomers have measured the abundance of helium throughout our galaxy and in other galaxies 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 rapidly moving particles of numerous different kinds). It doesn’t 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 remains 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 percent. The universe has not existed long enough for this figure to be significant 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 old, no helium could have existed. Calculations indicate that before this time temperature 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 so sufficiently that neutrons and protons could stick together. But the nuclear reactions that led to the formations of helium went on for only relatively short time. By the time the universe was a few minutes old, helium production had effectively ceased.
What does the passage mainly explain?
A. How stars produce energy
B. When most of the helium in the universe was formed
C. Why hydrogen is abundant
D. The difference between helium and hydrogen
Giải bởi qa.haylamdo.com
Kiến thức: Đọc hiểu
Giải thích:
Đoạn văn chủ yếu giải thích điều gì?
A. Các vì sao tạo ra năng lượng như thế nào
B. Thời điểm mà hầu hết khí heli trong vũ trụ được hình thành
C. Tại sao hydro lại dồi dào
‘ D. Sự khác biệt giữa heli và hydro
Thông tin: The universe has not existed long enough for this figure to be significant 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 old, no helium could have existed. Calculations indicate that before this time temperature 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 so sufficiently that neutrons and protons could stick together. But the nuclear reactions that led to the formations of helium went on for only relatively short time. By the time the universe was a few minutes old, helium production had effectively ceased.
Tạm dịch: Vũ trụ đã không tồn tại đủ lâu để con số này là lớn hơn đáng kể. Do đó, nếu vũ trụ là có phần hơn 25 % Heli bây giờ, thì nó phải có được khoảng 25% Heli tại một thời điểm gần lúc nó hình thành.
Tuy nhiên, khi vũ trụ hình thành chưa đầy một phút, Heli đã không thể tồn tại. Các tính toán cho thấy rằng trước khi nhiệt độ thời gian này là quá cao và các hạt của vật chất đã được di chuyển xung quanh nhiều quá nhanh. Chỉ sau mốc một phút Heli mới thể tồn tại. Đến thời điểm này, vũ trụ đã quá nguội đến nỗi Nơtron và Proton có thể kết hợp vào nhau. Nhưng phản ứng hạt nhân dẫn đến sự hình thành của Heli đã hoàn thiện trong một thời gian tương đối ngắn. Sau khi vũ trụ được hình thành vài phút, việc tạo ra Heli đã không còn hiệu quả.
Chọn B
With greatly increased workloads, everyone is _______ pressure now.
Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correct word or phrase that best fits each of the numbered blanks.
Everyone wants to reduce pollution. But the pollution (30) ______ is as complicated as it is serious. It is complicated because much pollution is caused by things that benefit people. (31) ______, exhaust from automobiles causes a large percentage of air pollution. But the automobile provides transportation for millions of people. Factories discharge much of the material that pollutes the air and water but factories give (32) _______ to a large number of people.
Thus, to end or greatly reduce pollution immediately, people would have to (33) ______ using many things that benefit them. Most of the people do not want to do that, of course. But pollution can be gradually reduced in several ways. Scientists and engineers can work to find ways to lessen the amount of pollution that such things as automobiles and factories cause. Governments can pass and enforce laws (34) ______ require businesses and traffic to stop, or to cut down on certain polluting activities.
Điền vào ô 34
Mark the letter A, B, C or D on your answer sheet to indicate the sentence that is closest in meaning in the sentence given in each of the following questions.
It is over twenty years since I last got in touch with them.
Mark the letter A, B, C or D on your answer sheet to indicate the most suitable response to complete each of the following exchanges.
: John and Alice are talking about going to the movie.
John: “I was wondering if you’d like to go to a movie tonight.”
Alice: “_______ What’s playing?”
Mark the letter A, B, C or D on your answer sheet to indicate the word(s) OPPOSITE in meaning to the underlined word(s) in each of the following questions.
Workers are always advised to be cautious when entering and leaving the place due to a recent fire.
Mark the letter A, B, C or D on your answer sheet to indicate the word or phrase that is CLOSET in meaning to the underlined part in each of the following questions.
Since her parents’ death, she has been brought up by her uncle.
Mark the letter A, B, C or D on your answer sheet to indicate the sentence that is closest in meaning in the sentence given in each of the following questions.
It is not until a Vietnamese girl getting 18 years old that she is allowed to get married legally.
I _______ along the street when I suddenly heard footsteps behind me.
Some films about violence have badly _______ children and teenagers.
Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correct answer to each of the questions.
By adopting a few simple techniques, parents who read to their children can considerably increase their children’s language development. It is surprising, but true. How parents talk to their children makes a big difference in the children’s language development. If a parent encourages the child to actively respond to what the parent is reading, the child’s language skills increase.
A study was done with two or three-year-old children and their parents. Half of the thirty children participants were in the experimental study; the other half acted as the control group. In the experimental group, the parents were given a two-hour training session in which they were taught to ask open-ended questions rather than yes-no questions. For example, the parent should ask, “What is the doggy doing?” rather than, “Is the doggy running away?” Experimental parents were also instructed how to expand on their children’s answer, how to suggest alternative possibilities, and how to praise correct answers.
At the beginning of the study, the children did not differ on levels of language development, but at the end of one month, the children in the experimental group were 5.5 months ahead of the control group on a test of verbal expression and vocabulary. Nine months later, the children in the experimental group still showed an advance of 6 months over the children in the control group.
What conclusion can be drawn from this passage?
Mark the letter A, B, C or D on your answer sheet to indicate the word that differs from the other three in the position of the primary stress in each of the following questions.
Mark the letter A, B, C or D on your answer sheet to indicate the sentence that is closest in meaning in the sentence given in each of the following questions.
“No, it’s not true. I didn’t steal the money!” Jean said.
