The island,  ____ to the mainland by a  bridge, is easy to go to.     [ ]

A. joining                                

B. to join    

C. joined                                  

D. having joined

照准部水准管轴垂直于竖轴的检校目的是使水准管轴垂直于竖轴,水准管气泡居于时,水平度盘成水平位置。