英语翻译：如果你昨天来参加聚会的话,你就会见到她（if)

You can meet she if you joined the party yesterday .

If you had come to the party, you would have seen her.
对过去情形的假设，if从句用过去完成时，主句用情态动词+完成时

If you came to the party yesterday,you would have seen her

if you were at the meeting yesterday, you would have seen her

如果你昨天来参加聚会的话,你就会见到她
If you had came to/attended/taken part in the party yesterday,you would have seen her
用虚拟语气
有不会的可以再问我

If you come to the party yesterday, and you will see her

you would have meet her if you had taken part in the party.
虚拟语气对过去时的虚拟。