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