They put their books in the backpack.对划线部分提问.
问题描述：
They put their books in the backpack.对划线部分提问.
划线部分是：in the backpack.
________ ________ __________ __________their books.
划线部分是：in the backpack.
________ ________ __________ __________their books？
答
Where do they put their books