is it possible to say THESE ARE FRUIT?
As far as I know fruit can be either a countable noun or an uncountable noun.
For example, when I would like to talk about fruits in general, I can say "There are abundance of tropical fruits in my hometown." (Fruit is a countable noun in this case)
On the other hand, I can say "I usually have one piece of fruit after meals." (Fruit is an uncountable noun in this case)
I saw the sentence "THESE ARE FRUIT" in a book. And I'm wondering whether it is a correct sentence or not. Please let me know.

(*) Besides, please tell me if there is any mistake in my question.

Question

is it possible to say THESE ARE FRUIT?
As far as I know fruit can be either a countable noun or an uncountable noun. 
For example, when I would like to talk about fruits in general, I can say "There are abundance of tropical fruits in my hometown." (Fruit is a countable noun in this case)
On the other hand, I can say "I usually have one piece of fruit after meals." (Fruit is an uncountable noun in this case)
I saw the sentence "THESE ARE FRUIT" in a book. And I'm wondering whether it is a correct sentence or not. Please let me know.

(*) Besides, please tell me if there is any mistake in my question.

Answer

Hi, fruit is a singular and plural noun, so an orange is a fruit and that pile of oranges is fruit. We don't normally add 's' to make it plural as you do in your question, though there is a phrase: 'fruits of labour' - don't ask me: English!

Answer

When "fruit" is used as a countable, it normally means type of fruit.  Your sentence could be:

"There is an abundance of tropical fruits in my hometown, including peaches and mangoes."
(abundance is countable)

If you simply meant all tropical fruit, without distinction, then you would just use "tropical fruit."

Answer

Thank you for your kind help, Helen!

Answer

Sure, you could say 'these are fruit, those are not.'