太阳消失在一片云后面。

The sun ___disappeared behind a cloud.

我们找过她，但她已经消失在人群中了。

We looked for her but she had ___disappeared into the crowd.

他们看到了我母亲在楼梯上的影子，然后就消失了。

They saw my mother's shadow [on] the stairs and ___disappeared.