In our factory there are 2,000 workers, two thirds of _____ are women. [ ]

A. them

B. which

C. whom

D. who

已知地球的质量为M，万有引力恒量为G，地球半径为R。用以上各量表示在地球表面附近运行的人造地球卫星的第一宇宙速度v＝　　　　。