The correct answer is: A. Low-pass
A low-pass filter is a filter that passes low frequencies and attenuates high frequencies. The pole-zero pattern of a low-pass filter is a circle in the complex plane centered at the origin. The radius of the circle determines the cutoff frequency of the filter.
A high-pass filter is a filter that passes high frequencies and attenuates low frequencies. The pole-zero pattern of a high-pass filter is a circle in the complex plane centered at infinity. The radius of the circle determines the cutoff frequency of the filter.
An all-pass filter is a filter that does not attenuate any frequencies. The pole-zero pattern of an all-pass filter is a straight line through the origin.
A band-pass filter is a filter that passes frequencies within a certain range and attenuates frequencies outside of that range. The pole-zero pattern of a band-pass filter is a pair of complex conjugate poles inside a circle in the complex plane. The radius of the circle determines the cutoff frequencies of the filter.
In the figure, the pole-zero pattern is a circle centered at the origin. This indicates that the filter is a low-pass filter.