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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. The residence time is the average length of time that any particular molecule of water remains in the lake, 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.

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

Ȍ}҂֪팦the length of time a given molecule of water remains in a lake Ȼͨ^λҵԭİ팦ľԭһԒĺ䣬“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.”ԒԷֳ̖ǰɂ־ǰһ־ҲҪǰһ־“The residence time is an averageͣrgƽ”@ϢcҪӛסٰѺ俴“the time spent in the lake by a given molecule would depend on the route it tookһӵˮͣںĕrgȡQߵ·”[˼ˮͣںĕrgDz̶ߵ·ֱtͣrgߵ·ѭh(hun)tͣrgLY(ji)ǰһ־ɵóY(ji)Փһӵˮͣںĕrgܱresidence time LҲܱʴ𰸞C

ͨ^v}ſ܉(j)ķ֮팦ľģtY(ji)Č(j);팦ľDzt(j)N(yn)ڱ

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