"是用on the first floor 因为floor是名词 那at呢?

"是用on the first floor 因为floor是名词 那at呢 "是用on the first floor 因为floor是名词 那at呢? at the first floor还是on the first floor “住在第一层”是live on the first floor还是live on first floor my classrom is ?the first floor 答案是on还是at on the first floor是什么意思 是on fifth floor还是on the fifth floor? 是in the fifth floor还是on the fifth floor on the first floor 中为什么要用“first”序数词呢 On just()at the floor! The canteen is on the first floor. The supermarket is on the first floor.