彩色多普勒血流显像仪的调节操作，下列哪项是错误的（）。

A.不调节速度标尺

B.调节彩色增益

C.调节滤波

D.调节取样容积

E.调节取样框大小

For many years, people（）electric cars. However, making them has been more difficult that predicted.

A.had dreamed of

B.have dreamed of

C.dreamed of

D.dream of