例句：

　　The plane disappeared behind a cloud.

　　飛機(jī)消失在云層里。

　　The sun went behind a cloud.

　　太陽(yáng)躲在了一朵云的后面。

　　Fog and low cloud cover are expected this afternoon.

　　預(yù)計(jì)今天下午有霧和低空云層。