At PM 3 o'clock, at the station, let's meet. [Syntax]

The correct answer is "あい". This is the verb stem of "あいます" (to meet). To make a suggestion or invite someone, Japanese uses the volitional form, which is created by attaching "ましょう" to the verb stem. Therefore, "あいましょう" correctly means "Let's meet," forming a polite invitation in the sentence. The verb stem is the core part that remains when removing the -masu ending.

正解は「あい」です。動詞「あいます」の語幹（ごかん）です。「～ましょう」と組み合わせて「あいましょう」（会いましょう）という誘い（さそい）の形になります。