请教一些初中英语语法知识1.什么叫做if后面不可以跟动词但whether可以?2.older是否不可以做定语?如果可以的

1.应该是说：if后面不能直接加不定式短语,但是whether可以.
即可以说：whether to do sth,而不能说：if to do sth.
意思是“是否做某事”.
如：I haven't decided whether to go with you.
我还没有觉得是否和你一起去.
2.older既可作定语,也可作表语,但是elder不能做表语,一般只做定语.
如：He is my older/elder brother.他是我哥哥.
He is older than Tom.他比汤姆更大.
不能说成：He is elder than Tom.
3.系动词的确没有被动语态.
4.没有.可以用短语比如说：sometime in the past/future
5.if从句中,some不是都要改成any的.此时,如果表示“一些”多用some,如果表示“任何”用any.
if从句中当然可以使用some的复合不定代词.
如：Please ask me if you have some questions.
Please ask me if you have any question.
If there is somebody in the room,please tell me.
6.没有have not to do sth的用法.
don't have to do sth 不必做某事 = needn't do sth = don't need to do sth