Two sinusoidal signals of same amplitude and frequencies $10 \; \mathrm{kHz}$ and $10.1 \; \mathrm{kHz}$ are added together. The combined signal is given to an ideal frequency detector. The output of the detector is
- $0.1 \; \mathrm{kHz}$ sinusoid
- $20.1 \; \mathrm{kHz}$ sinusoid
- a linear function of time
- a constant