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.
Line Astronomers have measured the
abundance of helium throughout our galaxy and in
(5) 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
(10) 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
(15) 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.
(20) 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
(25) 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.
Questions
13. What does the passage mainly explain ?
(A) How stars
produce energy
(B) The difference between
helium and hydrogen
(C) When most of the helium in
the universe was formed
(D)
Why hydrogen is abundant
14. 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 quasars
15. The word "constituents" in line 7 is closest in
meaning to
(A)
relatives (B) causes
(C) components (A) targets
16. Why does the author mention "cosmic rays" 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
began
(A) To explain the abundance of
hydrogen in the universe
17. The word "vary" in line 10 is closest in meaning to
(A) mean
(B) stretch
(C) change
(A) include
18. The creation of helium within stars
(A) cannot be measured
(B) produces energy
(C) produces hydrogen as a
by-product
(A) causes helium to be much
more abundant in old stars
than in young stars
19. The word "calculated" in line 15 is closest in
meaning to
(A) ignored
(B) converted
(C) increased
(A) determined
20. Most of th helium in the universe was formed
(A) in interstellar space
(B) in a very short time
(C) during the first minute of
the universe's existence
(A) before most of the hydrogen
21. The word "ceased" in line 26 is closest in meaning
to
(A) extended
(B) performed
(C) taken hold
(A) stopped
Please tally your answer with the below provided answers and
then comment here how much you got!
Answers
13. C 14. A 15. C 16. A 17.
C 18. B 19. A 20. B 21. A
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