Wires and wireless channels carry analog signals such as continuously varying voltage, light intensity, or sound intensity. How do we send digital information?

A we must devise analog signals to represent bits. we use a process of converting between bits and signals called digital modulation

B by using more than two signaling levels

C by using the NRZI (non-return-to-zero inverted) coding

D by balancing the signals so they have as much positive voltage as negative voltage