We cannot figure out quite a number of insects birds and animals are dying out.A. thatB.

问题补充：

We cannot figure out quite a number of insects, birds, and animals are dying out.

A. that

B. as

C. why

D. when

答案：

A. that

B. as

(答案→)C. why

D. when

解析：：figure out=understand by thinking. 理解。从句意看我不明白大量物种正在消亡，缺少状语，排除A、B项。从are dying out的时态排除D项，应该是我不明白大量物种为什么正在消亡。

【标签】名词性从句连接词