他还活着全靠运气。

　　John said that he was leaving for London on Wednesday.

　　约翰说他星期三要去伦敦。

　　(2)that在引导名词性从句时，常可省略，但在以下情况中，that不宜省略。

　　①that引导的主语从句位于句首时，that不可省略。

　　②当动词后带有两个或两个以上that引导的宾语从句时，只有第一个that可以省略，从第二个从句开始that不可省略。

　　③当that宾语从句前有it作其形式宾语时，that不可省略。

　　④that引导的从句作介词的宾语时，that不能省略。

　　⑤引导表语从句和同位语从句时，that一般不可省略。

　　The teacher told the students (that) they should hand in their homework the next day and that the homework must be signed by their parents.

　　老师告诉学生要在第二天上交作业，并且作业必须由家长签名。

　　The fact that he has fully recovered makes me feel good.

　　他已痊愈，真令我高兴。

　　2．whether/if

　　(1)if，whether引导的名词性从句是由一般疑问句或选择疑问句转化而来的，whether与if表示"是否"，只起连接词的作用，引导从句，在从句中不作任何成分。

　　(2)whether和if有时可通用，但在下列情况下，只可用whether：

　　①whether引导主语从句并放在句首。

　　②引导表语从句、同位语从句。

　　③whether从句作介词宾语。

　　④从句后有"or not"。

　　⑤后接动词不定式时。

　　Whether there is life on the moon is an interesting question.

　　月球上有没有生命是个有趣的问题。

　　The question is whether she should have a low opinion of the test.

　　现在的问题是她是否应该对这次测试有较低的评价。

　　Everything depends on whether we have enough money.

　　一切要看我们是否有足够的钱。

　　[即时演练1]　用that/whether/if填空

　　①That the college will take in more new students this year is true.

　　②Whether he can finish this task on time is of great importance.

　　③The students asked the question if/whether the book was worth reading.

④Let me know whether or not you can come.