神经细胞复极化的离子机制是（）
A.K+内流
B.K+外流
C.Na+内流
D.Na+外流
E.Ca2+内流
参考答案：B
I regret not having taken your advice. Otherwise I _____ this mistake.
[ ]
A. didn't make
B. would not make
C. hadn't made
D. wouldn't have made
读“某地等高线地形图”（单位：米），完成下列问题。
ab段河流流向是（）
A．由东向西
B．由东北向西南
C．由西南向东北
D．由南向北
