You      scold such a pupil who always keeps silent so seriously that

you     hurt him.

A．should; can

B．may; will

C．mustn’t ; may

D．can’t must

彩色多普勒诊断下肢静脉瓣功能不全的根据是：

A．静脉血流速度增快

B．静脉血流速度减慢

C．静脉血流信号不连续

D．在远端加压时出现持续1 秒的反向血流

E．静脉血流信号变细