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