液压传动可以在较大速度范围内实现（）。
A、有级变速
B、无级变速
C、恒速
参考答案：B
----- As we know, you won’t go back to the USA since you have established a research center here．But how long _____ in America?
----- For almost 10 years．
A．did you study
B．have you studied
C．were you studying
D．have you been studying
增强文化整体实力和竞争力要坚持把（）放在首位。
A.构建现代文化产业体系
B.社会效益
C.文化产品的丰富
D.经济效益
