一颗人造卫星以地心为圆心做匀速圆周运动,它的速率、周期跟它的轨道半径的关系( )
A:半径越大,速率越小,周期越大
B:半径越大,速率越大,周期越大
C:半径越大,速率越小,周期越小
D:半径越大,速率越小,周期不变
加拉帕戈斯群岛上不同地雀的形成过程是( )
—Why didn't your sister talk with me?
—She is a _______ girl. She is afraid of speaking before strangers (陌生人).