虚拟条件句中if的省略及倒装,had 是指哪个had?从句中有should,were,had三个助动词可以把if省略,并将这三个词提至句首.had是哪个had 如：If I had had time,I would have run round that lake again.如果指的是第一个had ,那表示与过去相反的都可以这样变了?

第一个，是的
提前的had是情态动词 第二个had是实义动词

在if从句中,如果含有“were,should,had’’时,可省去if而将“were,should,had’’置于句首,构成倒装句.例如：
Were l in your position,1 would go．如果我处在你的位子上,我就走了.
Had you arrived five minutes earlier,you could have seen them off．如果你早到五分钟,
你就可以给他们送行了.
Should he come,tell him to ring me up．如果他来的话,叫他打电话给我.
HAVE这个词比较特殊.had作为实义动词是能提前的.比如一般疑问句问实意动词时通常要加助动词DO.比如DO you like English?但HAVE就可以用两种方式表达.have you a pen?= do you have a pen?
不过,一般情况下.根据旧语法,非常严格的时候,Had I time这样的方式还是不要用.最好用if i had time.你知道它没错就行了
.你自己用的时候还是用普通的吧.