The pole-zero plots of three discrete-time systems $P, Q$ and $R$ on the $z$-plane are shown below.
Which one of the following is TRUE about the frequency selectivity of these systems?
- All three are high-pass filters.
- All three are band-pass filters.
- All three are low-pass filters.
- $P$ is low-pass filter. $Q$ is a band-pass filter and $R$ is a high-pass filter.