The Birthday Cake Lesson 5: Classify items into three categories, determine the count in each, and reason about how the last number named determines the total.

Who is one of the relative pronouns that exist in the English language. Pronouns are words that replace nouns, and relative pronouns are used to connect a clause or phrase to a noun or pronoun, and introduce adjectival clauses, for example:

The man who is standing at the door.  

In this sentence, the relative pronoun who is used to add information to identify the person I am referring to, in other words, I am not talking of any man, but the one standing at the door.  

The are other relative pronouns, such as: whom, which, whoever, whomever, whichever, and that. Who and whom are used for people, and which for things, as well as that can be used either for people or things too.  

The pronoun who can also be classified as an interrogative pronoun, and it may be used to form questions or indirect questions. The interrogative pronouns are five: what, which, who, whom, and whose. The pronouns who and whom are used to ask questions about people, such as:

Who was driving the car?