在比转速增大的过程中，要满足流量增大，扬程变小，水泵叶轮的结构应该是外径变小，叶片宽度（）。
A、不变
B、变大
C、变小
D、先变大后变小
参考答案：B
Kate is said ________ abroad, but I don’t know what country he studied in.
A．to have studied
B．to study
C．to be studying
D．to have been studying
药用植物DNA分子鉴定
