如果你早点起床，就能赶上早班车。

___If you wake up early, you can catch the first bus.

我不知道他是否会来参加聚会。

I'm not sure ___if he will come to the party.

如果你能帮我关下门就太好了。

___If you could help me close the door, that would be great.

要是当时听你的建议就好了。

___If only I had listened to your advice back then!