A $1 \; \mathrm{kHz}$ sinusoidal signal is ideally sampled at $1500$ samples/sec and the sampled signal is passed through an ideal low-pass filter with cut-off frequencey $800 \mathrm{~Hz}$. The output signal has the frequency
- zero $\text{Hz}$
- $0.75 \; \mathrm{kHz}$
- $0.5 \; \mathrm{kHz}$
- $0.25 \; \mathrm{kHz}$