請問不可數名詞可以加s嗎?

[PDL]

cloud是不可數名詞, 那應該說:

There are clouds in the sky.

There is cloud in the sky.

謝謝.

[Glotynn]

I visit this forum once in a while. This question has existed here for over a month, but I wonder why nobody in the club has provided a help. Let me give it a try.

The noun "cloud" is countable in all cases except when it means:
5. Something that obscures.
6. Suspicion or a charge affecting a reputation.
(from Dictionary.com)

There are clouds in the sky. (o)
There is cloud in the sky. (x)
There is a cloud in the sky. (o)