B分词短语充当条件状语(分词短语本身就具有充当条件状语的功能)。
Given a certain opportunity, he could have shown more talent.(=If he had been given a certain opportunity, he could have shown more talent.)
C 上下文暗示条件。常用来表示不具备条件的连词,如:but, or 或otherwise等。
I would have failed but that you helped me.
(but表示让步关系,意为“除非,要不是”,常与that一起构成 but that,相当于if... not...)
I was so busy then, otherwise, I would have finished it.(If I hadn’t been busy then, I would have finished it.)
I might have given you more help, but I was too busy.
More water and the young trees couldn’t have died.(=If you had given them more water, the young trees couldn’t have died.)