如果你饿了，冰箱里有些三明治。

___If you're hungry, there are some sandwiches in the fridge.

我不确定他是否会来参加聚会。

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

如果你能帮我拿一下包，我会很感激。

___If you could help me with my bag, I'd be very grateful.

要是我们早点出发就好了。

___If only we had left earlier.