When he saw all his books here and there on the floor, he knew that something terrible .
A. lying; must have happened
B. lie; must happen
C. lay; might have happened
D. had lain; could have happen
网友回答
(答案→)A. lying; must have happened
B. lie; must happen
C. lay; might have happened
D. had lain; could have happen
解析：考查感官动词和情态动词。see sb./sth. doing sth.看到某物/某人正在做某事；books和lie是主动关系，故用lying；must have done“一定做了某事”，表示肯定的推测。故选A。