题目

When learning a new language, speakers often have non-native accents. Linguistic research suggests such accent is shaped by the speaker’s first language that they learned when growing up. Schepens’ team’s research puts new light on just how strong these effects can be.There’re similar researches from other scientists, but Schepens’ team analyzed a data set of more than 50,000 adults, who learned Dutch as their second or third languages. Besides, these adults came from more than 60 different first language backgrounds. These data were collected through a state exam administered by the已知地球半径为R，地面处的重力加速度为g，一颗距离地面高度为2R的人造地球卫星绕地球做匀速圆周运动，下列说法正确的是：（       ）A、卫星的加速度大小为                          B、卫星的角速度为C、卫星的线速度大小为                        D、卫星的周期为