Pronoun
Interrogative

Relative pronouns can be used in an interrogative setting as interrogative pronouns. Interrogative pronouns ask which person or thing is meant. In reference to a person, one may use who (subject), whom (object) or whose (possessive); for example, Who did that? In colloquial speech, whom is generally replaced by who. English non-personal interrogative pronouns (which and what) have only one form.

In English and many other languages (e.g. French and Czech), the sets of relative and interrogative pronouns are nearly identical. Compare English: Who is that? (interrogative) and I know the woman who came (relative). In some other languages, interrogative pronouns and indefinite pronouns are frequently identical; for example, Standard Chinese 什么 shénme means "what?" as well as "something" or "anything".
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