81. A 10-MHz carrier is AM-modulated by a symmetrical square wave with a period of 1 ms. The bandwidth (kHz) of a filter with a center frequency of 10 MHz required to transmit the square wave with the first five nonzero components (n = 1, 3, 5, 7, 9) of its Fourier components is most nearly: O A. 3 O B. 6 O C. 10 OD. 20 fc=10MHz =200806