请解释第二十八题（英语单选）

答案：A
翻译：读完这些书后,把它们放回到他们所在的地方.
1.where they belong是一个地点状语从句,类似于一个也做地点状语的介宾短语或副词,在句中当然也充当地点状语.
如：Put the books back (on your desk) after you have finished them.
Put the books back (there) after you have finished them.
Put the books back (where they belong) after you have finished them.
上面三个例句中,括号内部分都做地点状语,只不过第一个是介宾短语,第二个是副词,而第三个则是地点状语从句.
其中,where在地点状语从句也充当状语.
2.再如：I found my bike (on the playground).
I found my bike (where I had lost it).
There is a city (where there is a river).
There is a city (by a river).
3.而其他三个选项中：
B多了介词to；
C中which不能单独做belong的宾语（belong to...）；
D中修饰the place的定语从句they belong中缺少地点状语where（= to the place）,而不是只缺少the place.