判断组织兴奋性高低的指标是
A．阈电位
B．时值
C．收缩幅度
D．刺激强度变化率
E．刺激频率
参考答案：B
对于一级评价项目，小时浓度应至少获取当地（）小时浓度值。
A.8
B.5
C.4
D.3
—I paid him 200 yuan for the sneakers.
—Oh, he charged you too much. You _________ them with half the money.
A．could have bought
B．needn’t have bought
C．must have bought
D．wouldn’t have bought
