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

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

A.  that          B.  as           C.  why            D.  when

试题答案

C

解析:

本题考查宾语从句知识，figure out为及物动词，故此句为宾语从句，从句意得知连词在从句中作原因状语，故选why.