循环球式转向器由于在螺母、螺杆间用滚动摩擦代替滑动摩擦，所以传动效率高，一般最高可达

—I went to work on foot yesterday, though it was raining cats and dogs.

—You      a bus. You were likely to get a cold.

A．must have taken

B．would take

C．should have taken

D．could take

下列植物，（）是百合科植物。

A、莎草

B、麦冬

C、茑尾

D、春兰

One of my best friends was _______  of his possessions during his stay in a hotel .

A．lost

B．stolen

C．robbed

D．taken

反射波法检测桩身混凝土完整性系统（）

A.速度型传感器灵敏度应大于100mv/g，

B.频带宽度应不窄于10～1000Hz，

C.放大系统增益应大于60DB，

D.采样时间为50～1000s