どちら

バスと でんしゃ と どちら が やすいですか。

The correct answer is "どちら" (dochira). This is an interrogative pronoun meaning "which one (of two or more options)." It is used when asking to choose between items, like "バスとでんしゃと" (the bus and the train). It becomes the subject of the question when followed by "が." "でんしゃ" (densha) is the noun "train." "と" (to) is a particle meaning "and," used to list items. "が" (ga) is the subject-marking particle, which should follow "どちら."

正解は「どちら」です。二つの選択肢から選ぶときに使う疑問詞で、「バスとでんしゃと」のような並列の後に来ます。「でんしゃ」は名詞です。「と」は並列を表す助詞です。「が」は主語を示す助詞で、「どちら」の後に続きます。