To an Astronomer,what Is a "Standard Candle

Multiple Choice

To an astronomer,what is a "standard candle"?

A) A standard light source that can be placed in a telescope,to which the brightness of stars and other objects can be compared
B) Any type of object whose absolute magnitude is known
C) Any galaxy whose redshift has been measured accurately
D) An accurately defined brightness scale for stars and galaxies,such as the magnitude scale