We Can Identify Only a Fraction of All the Radio

We can identify only a fraction of all the radio pulsars that exist in our galaxy because

A) gas and dust efficiently block radio photons.
B) few swing their beam of synchrotron emission in our direction.
C) most have evolved to become black holes, which emit no light.
D) massive stars are very rare.
E) neutron stars have tiny radii and are hard to detect even with large telescopes.