2011年托福考试阅读理解全新模拟试题（5）
13.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
14.The word "constituents" in line 9 is closest in meaning to
（A） relatives
（B） causes
（C）components
（D） targets
15.Why does the author mention "cosmic rays t in line 10？
（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
（D） To explain the abundance of hydrogen in the universe
16.The word "vary" in line 14 is closest ill meaning to
（A） mean
（B） stretchwww.examｗ.com
（C） change
（D） include
17.The creation of helium within stars
（A） cannot be measured
（B） produces energy
（C） produces hydrogen as a by-product
（D） causes helium to be much more abundant In old stars than In young star：
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