cloud是可数名词还是不可数名词

　　The plane climbed until it was clear of the clouds.

　　飞机爬升直至穿出了云层。

　　The sky was full of dark masses of clouds.

　　天空中乌云密布。

　　A cloud of dust rose as the truck drove off.

　　卡车开过时扬起一片灰尘。

　　The sun disappeared behind a bank of clouds.

　　太阳消失在一大片云后面。

　　It was beginning to cloud over.

　　天空开始阴云密布。

　　The dark clouds in the sky meant that a storm was coming.

　　天空中的乌云预示暴风雨即将来临。