if only用法及其他1.if only的用法是不是：对过去虚拟,用过去完成时,对现在和将来虚拟用would +do?或could+do?2.定语从句中先行词有the one,是不是关系词一定用that?3.系动词是不是一定没有进行时?有没完成时?

1. 是
2. 对
3. 系动词可以有进行时，也可以有完成时．

if only 后面用虚拟语气哦

1.是的.用一个例子概括你看：
以你要求的几种时态的虚拟语气：我要是在这儿就好了.
现在时：If only I were here.
过去时：If only I had been here.
将来时：If only I would be here.
动词向前推一个时态.
2.不对,还可以用who,whom,whose,只不过可以省略
比如：
.--where is your english book?just see what a mess in your schoolbag!
--The one whose cover is red,it’s easy to find anyway .
The one (whom)you referred to is my son. 你指的那个人是我儿子
The one (that) you bought is much better.你买的那个比较好.
这里面省略了做宾语的引导词that /which/who(m),
3.不是,比如：I'm feeling better nwo.我现在感觉好点了.feel不就是用正在进行了.
相信我,我是英语六级,英语老师,嘿嘿.