管理信息系统通常可分为多个子系统，整体系统的结构为（）
A.网状结构
B.关系结构
C.层次结构
D.串行结构
参考答案：C
In the lecture, the professor told us _______ to protect the environment.[ ]
A. how important was it
B. how important it was
C. how important
D. how important was
二尖瓣狭窄大咯血的原因是
A．肺淤血B．肺水肿C．支气管静脉曲张破裂D．肺栓塞E．合并支气管扩张症
