液压系统蓄能器根据结构可分为（）三种。
A.弹簧式
B.充气式
C.活塞式
D.气囊式
E.气瓶式
参考答案：C, D, E
Was Bill played football well helped the blind man cross the street?
A．it; that; who
B．which; that; that
C．it; who; that
D．who; which; that
婴幼儿口腔保健应开始于（）
A.婴儿出生后
B.第一颗牙齿萌出后
C.孩子1岁以后
D.乳牙全部萌出后
E.幼儿园开始
