The Expo 2010 Shanghai China has been a successful event. If it _____ for one more week, we might have

visited all the pavilions. [ ]

A. continues

B. had continued

C. continued

D. has continued

外循环式的滚珠丝杠副中，滚珠在循环过程结束后通过螺母外表面上的_________或__________返回丝杠螺母间重新进入循环。