If the Milky Way Formed Stars at Approximately a Constant

Multiple Choice

If the Milky Way formed stars at approximately a constant rate over the last 14 billion years, what fraction of the M-type stars that ever formed in it can still be found as main-sequence stars today? (Note that M-type stars have a mass of approximately 0.5 M_SUN.)

A) 10 percent
B) 33 percent
C) 50 percent
D) 75 percent
E) 100 percent