1、It depends on weather if she will come back on time .
2、I asked him if he could do me a favor .
If与whether的区别:
1、If不能引导放于句首的主语从句,而whether可以。 2、引导表语从句用whether,不用if。 3、引导同位语从句用whether,不用if。 4、whether可以引导从句作介词的宾语,不用if 。 5、whether or not 连在一起可以,但if不可以。而 “whether-----or not = if -----or not”
同位语从句:
定义:在复合句中充当同位语的句子。 同位语从句用来对其前面的抽象名词进行解释说明,被解释说明的词和 同位语在逻辑上是主表关系。 同位语常见名词:fact, suggestion, advice, idea, decision, news, thought, hope, belief, truth, doubt, promise, possibility, truth, warning, message, reason, report, question,explanation, wish, problem等。 常见的连接词:that, whether, what, who, how, when, where等。 用法: The thought that I want to buy my mother a birthday gift makes me excited.that 引导的同位语从句,解释说明 thought,从句不缺成 分 There is some doubt whether he will come. whether 引导同位语从句,if 不能引导同位语从句 we haven’t made the decision where we are going to spend our vacation. 有时同位语从句可以不紧跟解释说明的名词后面。 The news is surprising that he won the match.