が

どれ ___ あなたの傘ですか。

The particle "が" (ga) marks the subject of a sentence. It's often used with interrogative words like "どれ" (which one), "誰" (who), or "何" (what) when asking to identify the subject. Here, it identifies "which one" as the umbrella.

助詞「が」は文の主語を示します。「どれ」「誰」「何」などの疑問詞と使い、特定のものや人を尋ねる際に使われます。例：「誰が来ましたか。」