Thereasonwhythedinosaursdiedoutremainsunknown.They

问题详情：

The reason why the dinosaurs died out remains unknown. They ______ by an enormous volcanic eruption.

A. would have killed                    B. might have been killed

C. should have been killed            D. must have killed

【回答】

知识点：虚拟语气与情态动词

题型：选择题