From a Theoretical Standpoint,what Is a Pulsar

Multiple Choice

From a theoretical standpoint,what is a pulsar?

A) a star that alternately expands and contracts in size
B) a rapidly rotating neutron star
C) a neutron star or black hole that happens to be in a binary system
D) a binary system that happens to be aligned so that one star periodically eclipses the other
E) a star that is burning iron in its core