With his soldiers ________ for months, the general became even more worried when he thought that the enemy might began another attack at dawn.

A．surrounded;

B．to surround;

C．surrounding;

D．being surrounded;

增大雷达的天线口径面积可以提高天线的增益和减小波束宽度，从而提高雷达探测弱降水区和晴空回波的能力，（）。

A.降低副瓣的电平

B.提高雷达功率

C.提高探测的角分辨率

D.提高探测距离的精度