The elements other than hydrogen and helium (氮气) 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.
除氢和氦之外的元素存在的数量非常少，因此准确地说宇宙中氦约占25%的重量，而氢则略少于25%。

Astronomers have measured the amount of helium throughout our galaxy(星系) and in other galaxies as well. Helium has been found in old stars, in relativelyyoung ones, and in the distant objects known as quasars. Helium nuclei have also been found in cosmic rays that fall on the earth(cosmic”rays” are not really a form of radiation;they consist of rapidly moving particles (颗粒) of numerous different kinds) . It doesn’t seem to make very much difference where the helium is found. Its
天文学家测量过我们星系及其他星系中的氦含量。氦被发现在老星体中、相对年轻的星体中，以及被称为类星体的遥远天体中。氦核也被发现在落在地球的宇宙射线中。

amount never seems to vary much. In some places, there may be slightly more of it;in others, slightly less, but the proportion of helium to hydrogen nuclei always remains about the same.
氦的数量似乎并不受影响。在一些地方可能会稍微多一些；在其他地方可能稍微少一些，但是氦核与氢核的比例总是保持大致相同的。

Helium is created in stars. In fact, nuclear reactions that turn 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.
氦是在恒星中产生的。实际上，将氢转变为氦的核反应占了恒星产生能量的大部分。然而，通过计算得出，这种方式生产的氦数量不会超过几个百分点。宇宙的存在时间还不够长以产生显著的更多氦。因此，如果现在宇宙中氦含量略多于25%，那么在早期某个时刻它必须接近25%。

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 sufficiently. 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.
然而，在宇宙不到一分钟的时间里，不可能存在氦。计算表明，在这个时间之前，温度太高，物质粒子移动得太快。只有在一分钟之后，氦才能存在。到了这个时候，宇宙已经足够冷却下来。但导致氦形成的核反应只持续了相对较短的时间。等到宇宙几分钟大时，氦的产生实际上已经停止。

1. According to the passage, helium is _.
   A. difficult to detect
   B. the oldest element in the universe
   C. a common element in quasars
   D. the second element in the universe in amount
   答案：C

2. Why does the author mention “cosmic rays”in paragraph 2?
   A. To explain how the universe began.
   B. As part of a list of things containing helium.
   C. As an example of an unsolved astronomical puzzle.
   D. To explain the abundance of hydrogen in the universe.
   答案：B

3. Most of the helium in the universe was formed _.
   A. in invisible space
   B. in a very short time
   C. before most of the hydrogen
   D. during the first minute of the universe’s existence
   答案：B