Only relative pronouns that provide essential information can be omitted. Robin White, whom I met at college, called me last week. Whom is a part of a nonessential clause and cannot be omitted.

They are introduced by a relative pronoun like 'that', 'which', 'who', 'whose', 'where' and 'when'. For example: I won’t stand by the man who smells of slime. In this example, the relative ...

They are introduced by a relative pronoun like 'that', 'which', 'who', 'whose', 'where' and 'when'. For example: I won’t stand by the man who smells of slime. In this example, the relative ...