None of the Pulsars Emit Pulses of Visible Light Because

None of the pulsars emit pulses of visible light because

A) pulsars are too hot to emit visible light.
B) pulsars contain black holes that won't let visible light escape.
C) the gravitational field of a pulsar is so great that the visible light emitted is redshifted.
D) pulsars are too far away for the visible light to be bright enough to be detected at Earth.
E) A few pulsars do emit visible light pulses.