SECTION 3Directions: Each passage in this group is followed by questions based on its cont
SECTION 3
Directions: Each passage in this group is followed by questions based on its content. After reading a passage, choose the best answer to each question. Answer all questions following a passage on the basis of what is stated or implied in the passage.
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.
The passage is chiefly concerned with
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