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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  21
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] It can be inferred from the passage that one reason scientists consider local water from the solar nebula a necessary ingredient in the earth’s oceans is that
选项 A、it is improbable that enough volume of water from comets existed to fill the earth’s oceans
B、the water from the solar nebula contains less deuterium than sea water
C、the water from the solar nebula existed close enough to the earth to participate in the accretion process
D、without the water from the solar nebula more xenon would otherwise exist in seawater
E、without the water from the solar nebula the earth’s oceans would probably have formed at an earlier time
答案 B
解析
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