与过去事实相反
若与过去事实相反,条件从句的谓语用过去完成时(had+过去分词),主句谓语用“should (would,could,might)+have+过去分词”：
If I’d left sooner,I’d have been on time.要是我早点动身,我就准时到了.(但我动身太迟了)
*我认为这里没必要特别去强调必需是过去分词,if i had have a chance,i would have worked harder.这句话也可能这样去理解,意思都是一样的.