She must play the piano for at least one hour.(对for at least one hour 提问)
问题描述：
She must play the piano for at least one hour.(对for at least one hour 提问)
答
为你解答.
She must play the piano for at least one hour.(对for at least one hour 提问)
How long must she play the piano?
她必须要弹多久钢琴?
解释：how long用于对时间长度提问.