例 He has made it clear that he will not give in. 他清楚地表明他不会屈服。

　　13、doubt用于肯定结构时，后面用whether/ if引导名词性从句；用于否定结构或疑问结构时，后面用that引导名词性从句。be sure 用于肯定句或疑问句时，后接that引导的名词性从句；用于否定句时，后接whether/ if引导的名词性从句。

　　例 We doubt whether/ if he can win the game.我们怀疑他是否能赢得这场比赛。

　 
　14、连接代词whoever，whatever，whichever可引导名词性从句，相当于anyone who, anything that等。他们也可以引导让步状语从句，相当于no matter who/ what/ which。

　　例 Whoever breaks the law should be punished. 任何违法的人都要受到惩罚。

　　二、高考链接

　　1. It is pretty well understood ___ controls the flow of carbon dioxide in and out the atmosphere today. (2003上海)

　　A. that B. when

　　C. what D. how

　　2. --- I think it’s going to be a big problem.

　　--- Yes, it could be.

　　--- I wonder ___ we do about it.(2002上海春)

　　A. if B. how

　　C. what D. that

　　3. You should make it a rule to leave things ___ you can find them often. (1999NMET)

　　A. when B. where

　　C. then D. there