主句與從句的動(dòng)作發(fā)生在不同的時(shí)間，這時(shí)主，從句謂語動(dòng)詞的虛擬語氣形式因時(shí)間不同而不同，這叫做混合條件句。

If you had asked him yesterday, you would know what to do now.

(從句與過去事實(shí)相反，主句與現(xiàn)在事實(shí)相反。)

If it had rained last night (過去), it would be very cold today (現(xiàn)在).