It’s difficult to these old books for some of them none of the classification.
A. look for; are belonging to
B. put up; belong
C. sort out; belong to
D. pick up; are belonged to
网友回答
A. look for; are belonging to
B. put up; belong
(答案→)C. sort out; belong to
D. pick up; are belonged to
解析：动词短语用法辨析。Look for 寻找；put up张贴，留宿；sort out分类；pick up捡起；用车接；无意中学会；接受信号；康复。恢复；染上…；belong to属于（没有被动语态，没有进行时）；句意：把这些旧书分类很困难，因为他们不属于任何一种类别。故C正确。