______ the students in our school go to college in their teens.

A．A good many

B．A great many of

C．A great deal of

D．A great deal

彩色多普勒血流显像技术检测主动脉瓣口血流，速度标尺应如何选择应用？

A、选择高速档 

B、选择低速档 

C、不需进行速度调节 

D、选择中等速度 

E、以上都不是