以下是引用祈晴坊主在2003-9-18 11:30:00的发言: 11. Water vapor evaporated from the ocean contains a greater proportion of oxygen-16 and a smaller proportion of the heavier oxygen-18 than does seawater. Normally, this phenomenon has no effect on the overall composition of the ocean, because evaporated seawater returns to the ocean through precipitation. During an ice age, however, a large amount of precipitation falls on ice caps, where it is trapped as ice.
Which one of the following conclusions about a typical ice age is most strongly supported by the statements above?
(A) The proportions of oxygen-16 and oxygen-18 are the same in vapor from seawater as in the seawater itself.
(B) The concentration of oxygen-18 in seawater is increased.
(C) Rain and snow contain relatively more oxygen-16 than they do in interglacial periods.
(D) During the ice age, more of the Earth's precipitation falls over land than falls over the ocean.
(E) The composition of seawater changes more slowly than it does in interglacial periods.
这题选B 可我觉得,The concentration of oxygen-18 应该是在ice里面多,才支持啊 因为seawater里面不是本身就多吗
Say, sea water contains oxygen-16 and oxygen-18. During ice age, vapor doesn't return to sea, greater proportion of oxygen-16 lost while ox-18 only lost smaller proportion, so proportion of Ox-18 in seawater increases. |