1. 由连接词that, whether引导的表语从句
从属连词that的用法：①无意义；②不充当成分。而whether有词义，意为“是否”。这时主句的主语常常是些抽象名词，如 question, trouble, problem, result, chance, suggestion, idea, reason 等。表语从句对主句主语进行说明、解释，使主语的内容具体化。
The reason for his absence is that he hasn’t been informed.
他缺席的原因是他没被通知。
The point is whether we should lend him the money.
关键在于我们是否应该借钱给他。
What she couldn’t understand was that fewer and fewer students showed interest in her lessons.
她不能理解的是越来越少的学生对她的课感兴趣。
误区警示
if不能引导表语从句。
