23. The number of mountain gorillas is declining with such rapidity that the population is one-half in the twenty years between a count made by George Schaller in 1960 and the one made by Dian Fossey in 1980.

(A) with such rapidity that the population is one-half

(B) with such rapidity that the population was one-half

(C) so rapidly the population divided in half

(D) so rapidly that the population was halved（D）

(E) in such rapidity that the population is halved

这题都没人问过.看来我够弱智的..哎..

问个时态, 这题时态前面is 后面 was.. 怎么理解呀? is declining so...that....was...? 感觉意思怪

The number of mountain gorillas is declining so rapidly that the population was halved in the twenty years between a count made by George Schaller in 1960 and the one made by Dian Fossey in 1980.

这是一个错综时态复杂句。

主语The number of mountain gorillas谓语 is declining （山里面大猩猩的数量正在减少，这是描述现在的情况）so rapidly that the population was halved in the twenty years （减少的如此之快，怎么快？如此快以至于在过去的二十年里面数量减少拉一半。）between a count made by George Schaller in 1960 and the one made by Dian Fossey in 1980.（再说明是哪二十年？1960--1980。）

所以选B