Although students are ________ to more, they typically know less and are less mature than the

generations before.[      ]

A. displayed

B. released

C. explored

D. exposed

当波源和观测者做相对运动时，观测者接收到的频率和波源的频率不通，其频率变化量和相对速度大小有关，这种现象叫做（）。多普勒天气雷达是利用多普勒效应来测量（）。