消火栓系统水枪喷射试验，水枪的充实水柱长度（）水枪喷嘴射出的射程。
A.信号阀
B.止回阀
C.安全阀
D.开关阀
参考答案：A
用所给单词的适当形式填空。
1. There is a little ______ (accident) in the street.
2. You must look both ways before _______ (cross) the street.
3. ______ (turn) left at the traffic lights.
4. He isn't badly _______ (hurt).
5. He can see the words _______ (clear) on the blackboard.
6. It's _______ (well) to help children to cross the road.
7. Don't _______ (park) in the wrong place.
8. We must never _______ (play) football in the street.
对兴奋性突触后电位的叙述，错误的是
A．突触前神经元释放兴奋性递质B．突触后膜产生去极化变化C．突触后膜对Ca2+通透性增加D．主要使突触后膜Na+内流E．兴奋只能由前膜向后膜传递
