Question

【题目】Exactly______ the potato was introduced into Europe is uncertain, but it was probably around 1565.

A. whether B. why

C. when D. how

Answer 1

【答案】C

【解析】考查主语从句的连接词。句意：准确的说，土豆是什么时候被传到欧洲的还不确定，但是可能在1565年左右。此处when引导主语从句并在从句中作主语。