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 stars that ever formed in it can still be found as main-sequence stars today? Note that M stars have a mass of approximately .

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