Grace goes to the library once a week.对once a week提问,

问题描述:

Grace goes to the library once a week.对once a week提问,

这句话的意思是Grace一周去一次图书馆.
once a week 就是每周一次的意思.对once a week 提问就是问Grace问图书馆的频率.
所以应该是 How often does Grace to the library?Grace多久去一次图书馆?

望采纳!