可数/不可数：N-VAR 云;云团
The sky was almost entirely obscured by cloud.
天空几乎完全被云所遮蔽.
the varied shapes of the clouds...
云朵各种各样的形状
不可数：N-COUNT (烟雾、尘土等的)一团
The hens darted away on all sides, raising a cloud of dust.
一群母鸡四处乱窜,搅起一团尘土.
cloud是集合名词吗?具体用法是什么?
可数/不可数：N-VAR 云;云团
The sky was almost entirely obscured by cloud.
天空几乎完全被云所遮蔽.
the varied shapes of the clouds...
云朵各种各样的形状
不可数：N-COUNT (烟雾、尘土等的)一团
The hens darted away on all sides, raising a cloud of dust.
一群母鸡四处乱窜,搅起一团尘土.