By whatever means, a lake is constantly gaining water and losing water: its water does not just sit there, or, anyway, not for long. This raises the matter of a lake’s residence time.
, and it is calculated by dividing the volume of water in the lake by the rate at which water leaves the lake. The residence time is an average; the time spent in the lake by a given molecule (if we could follow its fate) would depend on the route it took: it might flow through as part of the fastest, most direct current, or it might circle in a backwater for an indefinitely long time.
7. It can be inferred from paragraph 4 that the length of time a given molecule of water remains in a lake
A.depends entirely upon the average speed of a lake' s currents
B.can be measured by the volume of the lake alone
C.can be greater or lesser than the residence time
D.is similar to the length of time all other molecules remain in that lake
答案是Ｃ，可是我想問的是Ｄ
Ｄ的意思是“與其他所有的粒子停留在湖時間的長度相似”嗎？
Ｄ是錯在哪呢？Ｃ的答案反而我覺得沒那麼適合太多。
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, and it is calculated by dividing the volume of water in the lake by the rate at which water leaves the lake. The residence time is an average; the time spent in the lake by a given molecule (if we could follow its fate) would depend on the route it took: it might flow through as part of the fastest, most direct current, or it might circle in a backwater for an indefinitely long time.
7. It can be inferred from paragraph 4 that the length of time a given molecule of water remains in a lake
A.depends entirely upon the average speed of a lake' s currents
B.can be measured by the volume of the lake alone
C.can be greater or lesser than the residence time
D.is similar to the length of time all other molecules remain in that lake
答案是Ｃ，可是我想問的是Ｄ
Ｄ的意思是“與其他所有的粒子停留在湖時間的長度相似”嗎？
Ｄ是錯在哪呢？Ｃ的答案反而我覺得沒那麼適合太多。
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