⑤whether常与or连用表示一种选择，if不能这样用；whether也可与动词不定式连用但if不能。如：The question of whether they are male or female is not important.
I have not decided whether to go or not.
⑥间接引语位于句首时或者是间接引语提前时用whether不用if.如：
Thank you， but whether I’ll be free I’m not sure at the moment.
⑦whether可引导一个让步状语从句表示“不管”、“无论”，而if不能。如：
Whether he comes or not， we will begin our party on time.
（3）疑问词 ever和no matter 疑问词的区别。
①疑问词 ever可引导名词性从句，在主从句中要充当一定的部分。如：
Whoever breaks the rule must be punished.
You can choose whatever you like in the shop.
②疑问词 ever还可引导让步状语从句。如：
Whoever breaks the rule， he must be punished，
Whatever you do， you must do it well.
③no matter 疑问词只能引导让步状语从句。如：
No matter what you do， you must do it well.
No matter who breaks the rule， he must be punished.
（4）when和where引导的同位语从句与定语从句的区别。
when 和where前面的名词若是表示时间、地点的名词，则when和where引导的是定语从句，否则则为同位语从句。如：
They put forward the question where they could get the money.
This is the place where the accident happened.
2、名词性从句中主句和从句的时态一致
（1）宾语从句中主句和从句的时态保持一致，但如果从句中表示提示的是客观现象，虽然主句是过去时态，从句仍用一般现在时。如：
Hello，I didn’t know you were in London. How long have you been here？