As an experienced technician， you are responsible for Technical Support. A customer calls to askthe best signal level and noise level for cell phone. How to respond？（） A:  -40dBm signal and -90dBm noise B:  -50dBm signal and -90dBm noise C:  -30dBm signal and -90dBm noise D:  -20dBm signal and -90dBm noise