锅水要保持一定的碱度，一般维持在（）毫克当量/升即可。
A.5
B.10
C.15
D.20
参考答案：B
30. “It is not only you but also Tom who _________,” said the teacher after knowing what had
happened.
A．are to be blamed
B．is to be blamed
C．are to blame
D．is to blame
机车、车辆车钩三态作用是指（）
A、全开位、半开位、闭锁位
B、闭锁位、开锁位、全开位
C、开锁位、闭锁位、半开位
