We cannot figure out quite a number of students were infected with the flu.A. that B. whe

问题补充：

We cannot figure out quite a number of students were infected with the flu.

A. that

B. when

C. why

D. where

答案：

A. that

B. when

(答案→)C. why

D. where

解析：考查名词性从句。句中why引导宾语从句，在从句中作原因状语，故选C。