For a bit-rate of $8 \; \mathrm{kbps}$, the best possible values of the transmitted frequencies in a coherent binary FSK system are
- $16 \; \mathrm{kHz}$ and $20 \; \mathrm{kHz}$
- $20 \; \mathrm{kHz}$ and $32 \; \mathrm{kHz}$
- $20 \; \mathrm{kHz}$ and $40 \; \mathrm{kHz}$
- $32 \; \mathrm{kHz}$ and $40 \; \mathrm{kHz}$