双边带调制信号uDSB = 25cos2p ´ 103tcos2p ´ 106t mV，其载波的频率wc和调制信号的频率W分别为（　）。

A、wc = 2p ´ 103 rad/s，W =
2p ´ 106 rad/s;
B、wc = 2p ´ 106 rad/s，W
= 2p ´ 103 rad/s;
C、wc = 2p ´ 106 rad/s，W
= 2p ´ 106 rad/s;
D、wc = 2p ´ 103 rad/s，W
= 2p ´ 103 rad/s