From an Observational Standpoint,what Is a Pulsar

From an observational standpoint,what is a pulsar?

A) a star that slowly changes its brightness,getting dimmer and then brighter with a period of anywhere from a few hours to a few weeks
B) an object that emits flashes of light several times per second or more,with near perfect regularity
C) an object that emits random "pulses" of light that sometimes occur only a fraction of a second apart and other times stop for several days at a time
D) a star that changes color rapidly,from blue to red and back again
E) a star that rapidly changes size as it moves off the main sequence