缺乏静脉瓣的为（）
A.面上静脉
B.面前静脉
C.面后静脉
D.面总静脉
E.面下静脉
参考答案：B
I’m very glad to see that your vocabulary is gradually ________.
A．building up
B．turning up
C．coming up
D．waking up
写出事故浆液泵顺控停止步骤？
