いき

わたしは あした くるまで、がっこう へ いき ます。

The correct answer is "いき" (iki). This is the stem of the verb "いく" (iku, to go). It directly connects to the politeness suffix "ます" to form "いきます" (ikimasu), meaning "will go." This verb is essential for completing the action. "がっこう" (gakkou) is a noun for a destination. "へ" (e) is a particle indicating direction, it should follow a destination like "がっこうへ." "ます" (masu) is a politeness suffix that follows a verb stem, it cannot stand alone or precede the verb stem.

正解は「いき」です。「いく」の動詞の語幹で、「ます」とつながり「いきます」となります。「がっこう」は目的地を示す名詞で、「へ」は方向を示す助詞です。「ます」は動詞の語幹の後ろにつきます。