题目

 The nurse doesn't feel well today, _________ she still works very hard.A. but B. and C. or D. when 答案：A两颗人造卫星A、B绕地球做圆周运动，周期之比为TA : TB =" 1:" 8，则轨道半径之比和运动速率之比分别为A. RA : RB = 4:1;  VA : VB = 1:2      B. RA : RB = 4:1;  VA : VB = 2:1C. RA : RB = 1:4;  VA : VB = 1:2      D. RA : RB = 1:4;  VA : VB = 2:1