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  3. Comets are now known to contain twice as many atoms of deuterium to

Comets are now known to contain twice as many atoms of deuterium to

游客2025-02-22  6
问题              Comets are now known to contain twice as many atoms of deuterium to
       each atom of ordinary hydrogen found in seawater.  Scientists have also
       discovered that meteorites could not solely have delivered the water in the
Line     ocean, for then the earth’s atmosphere would contain nearly 10 times as much
(5)      xenon as it actually does, given that meteorites carry excess xenon. Hence, the
       best model for the source of the oceans at the moment is a combination of water
       derived from comets and water caught up in the rocky body of the earth as it
       formed. This mixture satisfies both the xenon and deuterium problem, the
       latter especially if the rocky material out near the earth’s present orbit
(10)     collected some regularly composed local water from the solar nebula before they
       accreted to form the earth. New laboratory studies have indicated that the
       water vapor in the solar nebula would have had a low enough proportion of
       deuterium to complement the excess deuterium found in comets. [br] The passage is chiefly concerned with
选项 A、explaining the process by which the Earth and its oceans accreted
B、reporting how recent research has arrived at a new explanation for the constitution of the Earth’s oceans
C、accounting for the chemical composition of the various ingredients of the Earth’s oceans
D、contrasting various competing hypotheses as to what the Earth’s oceans consist of
E、reporting inconsistencies with the result of new research into the composition of the Earth’s oceans
答案 B
解析
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