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How is a newborn star formed? For the answer to this question, we must look to the familiar physical concept of gravitat
How is a newborn star formed? For the answer to this question, we must look to the familiar physical concept of gravitat
admin
2012-01-15
148
问题
How is a newborn star formed? For the answer
to this question, we must look to the familiar
physical concept of gravitational instability. It is a
Line simple concept, long-known to scientists, having
(5) been first recognized by Isaac Newton in the late
1600s.
Let us envision a cloud of interstellar atoms
and molecules, slightly admixed with dust. This
cloud of interstellar gas is static and uniform.
(10) Suddenly, something occurs to disturb the gas,
causing one small area within it to condense. As
this small area increases in density, becoming
slightly denser than the gas around it, its gravita-
tional field likewise increases somewhat in
(15) strength. More matter now is attracted to the area,
and its gravity becomes even stronger; as a result,
it starts to contract, in the process increasing in den-
sity even more. This in turn further increases its
gravity, so that it accumulates still more matter
(20) and contracts further still. And so the process
continues, until finally the small area of gas gives
birth to a gravitationally bound object, a newborn
star.
The author provides information that answers which of the following questions? Ⅰ. How does the small area’s increasing density affect its gravitational field? Ⅱ. What causes the disturbance that changes the cloud from its original static state? Ⅲ. What is the end result of the gradually increas-ing concentration of the small area of gas?
选项
A、Ⅰ only
B、Ⅱ only
C、Ⅰ and Ⅱ only
D、Ⅰ and Ⅲ only
E、Ⅰ, Ⅱ and Ⅲ
答案
D
解析
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本试题收录于:
GRE VERBAL题库GRE分类
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GRE VERBAL
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