KY-310型牙轮钻机提升加压机构共有（）组链轮拖动回转小车运动。
A.五
B.六
C.七
D.八
参考答案：C
The chairman was about to declare the conference open ____ the lights went all out.
A．as
B．while
C．then
D．when
在腹部，脐中旁开0.5寸的腧穴是（）
A.膏肓
B.气海
C.大横
D.肓俞
E.天枢
