3．在肯定句中，名词doubt后的同位语从句用whether引导；在否定句或疑问句中，doubt后的同位语从句用that引导。

　　There is some doubt whether he will leave.

　　对于他是否离开有些疑问。

　　I have no doubt that he will win the game.

　　我坚信他会赢得这场比赛。

　　[即时演练2]　单句语法填空

　　①He gave orders that the work (should)_be_started (start) immediately.

　　②I have some doubt whether she will come on time.

　　③There can be little doubt that this kind of class can help the gifted children to graduate earlier.

　　④Word came that we would have lessons on Saturday.

　　四、同位语从句与定语从句的区别

从意义上看 从引导词上看 作用相当于 对先行词的作用 that wh­类引导词 同位语从句 名词 解释，说明 无意义，不作成分，不可省略 有意义，作成分，其前面无意义相当的先行词 定语从句 形容词 修饰，限制 that指代先行词，在从句中作主语、宾语、表语，作主语时不可省，有时可用which代替 有意义，作成分，其前面有意义相当的先行词； whether, how, what等不能用来引导定语从句 　　　　The fact that there is no life on the moon is known to us all.

　　月球上没有生命这个事实大家都知道。(同位语从句)

　　The fact that he often talks about is useless to us.

　　他经常谈论的这个事实对我们毫无用处。(定语从句)

　　[即时演练3]

　　判断加黑部分是定语从句还是同位语从句

　　①He will never forget the days when he lived with his grandparents.定语从句

　　②He has no idea when the meeting will be held.同位语从句

③We are glad at the news that he will come.同位语从句