First of all, I would like to thanks all of you ,and I would like to ask one more question.
(4) Well, I think there is a big difference:
(a) In "A friend of Tom/Tom's," please notice the word "a." (or "one").
Thus, if you choose to say "A friend of Tom's," that means something like:
One friend out of Tom's friends. By The Parser
I have understood that we can say: A friend of Tom or a friend of Tom's
Two friends of Tom's (It is ok).....It means 'two friends out of Tom's friends.
But what about mentioning about two or much more friends?
-Two friends of Tom. Is that ok or must we put 's' after Tom?