There are a lot of black clouds.It m_______ rain soon

There are a lot of black clouds.It m_______ rain soon
There are a lot of black clouds.It m_______ rain soon

There are a lot of black clouds.It m_______ rain soon
must
天空布满了乌云.雨不久就会来了.
表示对未来的猜测,用情态动词.

means