安全阀安装时，其方向一般应（）。
A.垂直向上
B.水平安装
C.垂直向下
D.轴向安装
参考答案：A
— I was just in time to get there for the meeting. Thank you for lending me the bike.
— __________.
A．That’s right.
B．Of course not.
C．You’re welcome.
D．The same to you.
先天性心脏病最常见的是
A．动脉导管未闭B．房间隔缺损C．室间隔缺损D．法洛氏四联症E．肺动脉狭窄
