LSAT－17－3－11

swimmingfrog

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.（B）

(E) The composition of seawater changes more slowly than it does in interglacial periods.

这题我做对了，可并不明白其中的逻辑关系。

hedonism555

less 16 in sea water = higher concentration of 18 in sea water ?   a common sense , right ?

jiechen

我也懂这个常理,但是文中说正常情况下这种现象不会影响海水的成分,通过降雨.  而在冰川时期,降雨不会返回到海中,我认为海水的成分改变,因此我觉得E对

jiechen

up

lawyer_1

1。the question asks the situation during the typical ice age when a large amount of precipitation falls on ice, not to sea, which creates less and less proportion of oxygen-16 in the sea water. because when water evaporated from the ocean, more proportion of oxygen-16 came out from sea water.

2. there is no any information concerning the situation in interglacial periods. In fact, according to the stimulus, overall composition of the ocean keeps constant because of the process of precipitation. Therefore, E is wrong.

jiechen

谢谢, 看了你的解释,我都不知道我原来为什么会选错,还挺自信的,真是的