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Hi, can you tell me which is correct? why?Thank you.

My favourite fruit is the strawberry (strawberry, a strawberry, strawberries)

I had vegetable (vegetables) for lunch.
I had tomato (a tomato, tomatoes) for linch
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Hello Guest

I'm myself a learner of English and I'm afraid I'm not qualified to advise you. But allow me to write a tip I have learned in school.

Your question is: "which one is better "a/an X" or "Xs" or simple "X" for food stuff?". One convenient way for the choice is to guess the quantity you would usually eat at a time.
My favourite fruit is the strawberry (strawberry, a strawberry, strawberries)
Do you eat only one strawberry at meal? Probably no. I guess you would eat more than several strawberries. So I think it sounds more natural to say :"My favorite fruit is strawberries." The noun "strawberry" is countable and so I would feel odd if I hear "My favorite fruit is strawberry".
I had vegetable (vegetables) for lunch.
"Vegetable" is a countable (a/an X or Xs) as well as a collective noun (only X). So in this case you can choose either. If I hear "I had vegetables for lunch", I would think you ate various kinds of vegetable.
I had tomato (a tomato, tomatoes) for lunch
In this case all the three are possible. If I hear "I had tomato for lunch", I would imagine you ate a tomato or more that were cut beforehand into pieces. If I hear "I had a tomato for lunch", I would think you ate a whole tomato of a relatively large size. If I hear "I had tomatoes for lunch", I would imagine you ate several tomatoes of small sizes.

You can get some useful information on this subject here: [url="http://www.onestopenglish.com/ProfessionalSupport/ask/vocabulary_thornbury_concord.htm"]Scot Thornbury: An Apple or Apples[/url]

I hope teachers or other native speakers would give better comments.

paco
Comments  
I think the correct one is :

My favourite fruit is strawberry.
I had vegetable for lunch.

Here strawberry/vegatable mean some kind of food.For the last sentence you can use any one , the sentence will have different meaning as well.
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My favourite fruit is strawberry (true)

you cant use "the" and "s"

I had vegetable for lunch (true)

you cant use "the" and "s" either

Because vegetable is uncountable.
 paco2004's reply was promoted to an answer.
Thank you all very much for helping me.
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