At first we didn’t know to do.A. how B. where C. when D. what

问题补充：

At first, we didn’t know to do.

A. how

B. where

C. when

D. what

答案：

A. how

B. where

C. when

(答案→)D. what

解析：A.how 如何 B.where哪里 C.when何时 D.what什么；句意：首先，我们不知道要做什么。what to do 做什么，故选D