Câu hỏi: Read the following passage and mark the letter A, B, C, or D to indicate the correct answer to each of the questions from 35 to 42
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 (cosmicrays 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 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 old, 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 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.
Why does the author mention "cosmic rays"?
A. To explain how the universe began.
B. To explain the abundance of hydrogen in the universe.
C. As part of a list of things containing helium.
D. As an example of an unsolved astronomical puzzle.
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 (cosmicrays 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 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 old, 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 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.
Why does the author mention "cosmic rays"?
A. To explain how the universe began.
B. To explain the abundance of hydrogen in the universe.
C. As part of a list of things containing helium.
D. As an example of an unsolved astronomical puzzle.
Kỹ năng: Đọc
Giải thích:
Tại sao tác giả lại đề cập đến "tia vũ trụ"?
A. Để giải thích vũ trụ bắt đầu như thế nào.
B. Để giải thích sự phong phú của hydro trong vũ trụ.
C. Là một phần của danh sách những thứ có chứa heli.
D. Như một ví dụ về câu đố thiên văn chưa giải quyết.
Giải thích: "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...": Helium đã được tìm thấy trong các ngôi sao cũ, ở những ngôi sao tương đối trẻ, trong khí liên sao và trong các vật thể ở xa gọi là chuẩn tinh. Hạt nhân helium cũng đã được thấy là thành phần của các tia vũ trụ rơi xuống trái đất...
Giải thích:
Tại sao tác giả lại đề cập đến "tia vũ trụ"?
A. Để giải thích vũ trụ bắt đầu như thế nào.
B. Để giải thích sự phong phú của hydro trong vũ trụ.
C. Là một phần của danh sách những thứ có chứa heli.
D. Như một ví dụ về câu đố thiên văn chưa giải quyết.
Giải thích: "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...": Helium đã được tìm thấy trong các ngôi sao cũ, ở những ngôi sao tương đối trẻ, trong khí liên sao và trong các vật thể ở xa gọi là chuẩn tinh. Hạt nhân helium cũng đã được thấy là thành phần của các tia vũ trụ rơi xuống trái đất...
Đáp án C.