刮板流量计无流量原因是管线压力为零、控制阀门关闭（）等。
A.转子有时卡住
B.螺母松动
C.轴不同心
D.转子轧住
参考答案：D
小公司效应支持市场有效性假说。
A. It is not enough to learn a foreign language for three years. B. It requires time and effort to master a foreign language. C. A child can learn a foreign language better if her mother is around. D. A child can learn a foreign language faster than an adult.
