A:speak
B:speaking
C:to speak
D:spoke
Each of us is looking forward _________ a good result. Let's do it more carefully.
一人造地球卫星绕地球做匀速圆周运动,假如该卫星变轨后仍做匀速圆周运动,速度减小为原来的一半,不考虑卫星质量的变化,则变轨前后卫星的( )