is from the same family of words as これ
, 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.
Which one is your car?
When there are only two choices to select between, どちら
, or どっち
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.