他开了一整天的车，所以一定累坏了。

He's been driving all day, so he ___must be exhausted.

食物都没了；他们一定把什么都吃光了。

There's no food left; they ___must have eaten everything.

那件事发生时，我大概七岁左右。

I ___must have been about seven years old when that happened.