A sinusoid x(t) of unknown frequency is sampled by an impulse train of period 20 ms. The resulting sample train is next applied to an ideal lowpass filter with a cutoff at 25 Hz. The filter output is seen to be a sinusoid of frequency 20 Hz. This means that x(t) has a frequency of

A continuous-time LTI system with system function H($$\omega$$) has the following pole-zero plot. For this system, which of the alternatives is TRUE?