As for me, the thing of song to sing is poor. [Syntax]

The correct answer is "うたう". This is the plain form of the verb "うたいます" (to sing). To express being good or bad at an action, the Japanese grammar pattern requires a verb in its plain form followed by のが. So, "うたうのが" correctly forms the phrase "the act of singing", which then precedes "へたです" (bad at) to complete the sentence. This structure is essential for describing proficiency in activities.

正解は「うたう」です。「うたいます」の普通形（ふつうけい）です。何かの動作が上手（じょうず）か下手（へた）かを言うときは、「動詞の普通形＋のが＋じょうず／へたです」という文法（ぶんぽう）パターンを使います。そのため「うたうのが」が正しいです。