They often stay up reviewing their lessons booksall over the desk.A. spreadingB. spreadC

问题补充：

They often stay up, reviewing their lessons, booksall over the desk.

A. spreading

B. spread

C. are spreading

D. to spread

答案：

A. spreading

(答案→)B. spread

C. are spreading

D. to spread

解析：books与spread之间是被动关系，spread的过去分词与原形一样。句意：他们常常熬夜，复习功课和看被铺满整个桌面的书本。