The only existing problem is we can find this special wood in the forest in such a short

问题补充：

The only existing problem is we can find this special wood in the forest in such a short time.

A. when

B. where

C. that

D. whether

答案：

A. when

B. where

C. that

(答案→)D. whether

解析：考查名词性从句。表语从句中是一般疑问句，句用关系词whether引导。句意：唯一存在的问题是，在这么短的时间内我们是否能够在森林里找到这种特殊的木材。根据句意说明D正确。