どれ is from the same family of words as
これ,
それ, and
あれ. These words are called こそあど言葉(ことば) in Japanese. Unlike the other 3, which all point to a specific thing, words starting with ど are designed for enquiring about something unknown.
どれ can roughly be translated as ‘which’ in English, and is used for enquiring about a group (of 3 or more things).
From these examples, we can see that the particle
が is often used with
どれ, especially when preceding questions. However, when
どれ follows a noun,
は will be used.
-
あなたの車(くるま)はどれ?
Which one is your car?
When there are only two choices to select between,
どちら +
の, or
どっち +
の will be used instead of
どれ. This is a habit that has become part of the language over time, and was not originally how these words were used.