井下安全阀分为（）。
A.油管回收式
B.钢丝回收式
C.活塞式
D.气管回收式
参考答案：A, B
The professor explained this theory so clearly that this phenomenon was easy enough ____. [ ]
A. for us to work out
B. working out
C. for working out
D. to working out
高血压的发病与哪项因素关系不大
A.遗传因素
B.肾因素
C.社会心理应激
D.每日饮食摄盐量过多
E.患动脉粥样硬化
