Dense Wavelength Division Multiplexing (DWDM) is an important innovation in optical networks.Which two descriptions best define DWDM?（）

• A、optical technology for transmitting up to 32 channels over multiple fiber strands
• B、optical technology for transmitting up to 16 channels over multiple fiber strands
• C、a WDM system that is compatible with EDFA technology
• D、a technology for transmitting more closely packed optical signals using more sophisticated transceiver designs than CWDM .