Help me again

[Emanuelli]

I'm not convinced yet of "countable nouns".
I mean, if a native speaker says: "I like strawberry" (as I've heard sometimes), should I consider that his/her English is not correct? Can I accept that?

Which is the correct way: "I have a doubt" or "I have some doubt".

Watermelon can be C or U. What's the difference?

Thanks.

[Casiopea]

"I like strawberry" (as I've heard sometimes), should I consider that his/her English is not correct? Can I accept that?

It depends on the context:

Pat: I like strawberries. (the fruit)
Max: I like strawberry. (the flavor)

Which is the correct way: "I have a doubt" or "I have some doubt".

I doubt. . .
I have some doubts. (Plural)

Watermelon can be C or U. What's the difference?

Count: How many watermelons do you have? (noun)
Cf. I like watermelon flavored ice-cream. (adjective)