Visitors can borrow the books inside for free.

参观者可以免费借阅里面的书。

A backpack is a pack that goes on your back, you see all kids wearing it to school, it zips open, you put your books inside and you wear it on your back.

背包是背在背上的包， 你看到所有孩子都背着它上学，它拉开拉链， 你把书放在里面， 然后背在背上。