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