相似连词辨析

　　⑴if与whether：①作“是否”讲，引导宾语从句，常互换。如：Do you know if/whether our teacher will come to the party? ②在介词之后、动词不定式之前或在or之前，只用whether。如：I can’t decide whether to go or not. ③if还作“如果”讲，引导条件状语从句。如：If Joan comes, I’ll tell you as soon as possible.
　　⑵because, since/as与for：①because意思是“因为”，because从句构成句子的主要部分，表示从、主句之间有必然的因果关系，可回答why问句。如：Ricky did not write to Kitty because he was very busy. —Why did Ricky work so hard? —Because he wanted the show to be a success. ②since意思是“既然”，常用于书面语中，as意思是“由于”，常用于口语中，表示对方已知的、较明显的原因。如：Millie asked me to go to her house since we are good friends. As we lost our umbrella in the wind, we had to walk in the snowstorm. ③for上述三个词均为从属连词，而for是并列连词，for分句只位于句末，前面有逗号，该分句是对前一分句所述情况做推测性的说明、解释。如：It’s going to rain, for there is much cloud in the sky.
　　⑶so…that…①so为副词，修饰形容词或副词。如：Hello Kitty danced so beautifully that everyone screamed. ②“so+形容词”后也可跟单数可数名词。如：He is so tall a boy that he is good at basketball. ③如果名词前有形容词many, much, few, litter等修饰，用so。如：There are so many people in the room that it is very noisy. such … that …：such为形容词，修饰名词。如：It was such a warm day that we all went swimming.