He sits / sat next to me. 哪個對?

My best friend called Tom. (It is grammatically correct, but it means my best friend telephoned Tom.)
My best friend who is called Tom. (Wrong - incomplete sentence. Where is the main clause? )

If you are still at school/university and Tom is your classmate, you can use the present tense.

My best friend is called Tom. He sits next to me in every lesson. (Correct)

Tom, my best friend, sits next to me in every lesson. (Correct – I think it is much better.)

My best friend (who is) called Tom. He sits next to me in every lesson.

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