英语语法1 定语从句中有些句子关系副词可以用on which in which 等替代那我怎么判断介词是用哪个例如I‘d

英语语法
1 定语从句中有些句子关系副词可以用on which in which 等替代
那我怎么判断介词是用哪个
例如I‘d like you to explain in the reason why(for which) you were absent.
为什么是用 for
2 虚拟语气的问题
当非真实条件句中有 should had 或were 使 可以省略 if
那什么是非真实条件句
能否用些通俗的语言讲解

1.定语从句的关系副词只有三个,即：when/where/why.
其中why是固定的,只能等于for which,用于修饰的先行词是reason(s).
因为这个固定短语：for...reason(s),意思是“因为...原因”.
如：I don't know the reason why he was late.
= I don't know the reason for which he was late.
其中：(why) he was late
= (for which) he was late
= he was late (for which)
= he was late (for the reason)
介词判断的方法是：把定语从句所修饰的先行词（名词或代词）放入定语从句,看用哪个介词能把先行词和定语从句结合成一个完整而且通顺的句子.
用on/in which可以换的只能是when/where.
如：I'll never forget the city where I stayed last year.
= I'll never forget the city in which I stayed last year.
其中定语从句变化为：where I stayed last year = in which I stayed last year = I stayed in which last year = I stayed in the city last year
再如：I like the island where we landed yesterday.
= I like the island on which we landed yesterday.
其中变化为：where we landed yesterday = on which we landed yesterday = we landed on which yesterday = we landed on the island yesterday
其他类似的句子：
I‘ll never forget the day when I stayed with you.
= I'll never forget the day on which I stayed with you.
句中含有on the day这个时间状语
I'll never forget the year when I stayed with you.
= I'll never forget the year in which I stayed with you.
句中含有in the year这个时间状语
2.非真实条件句,也就是说条件状语从句所表示的情况并不是真实的,而是虚拟出来的.
如：If I were you,I would leave right away.
I were you就是非真实的情况,因为“我不可能是你”.
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