Question

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 

Answer 1

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