You can take anything from the shelf and read, but please ________ the books when you've finished with them.
A.put onB.put downC.put backD.put off在线课程C
解析：
此题题意是“你可以拿书架上任何一本书，但看完后请放回原处”．此题考查的是由put所构成的一些短语的区别和用法．put on穿上，上演；
put down放下，记上；
put back放回；
put off推迟．