When he saw all his books here and there on the floor he knew that something terrible .

问题补充：

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

答案：

(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。