Cygnus X-1 and LMC X-3 are black holes if the masses of the unseen companions are
a. between 1.4 and 3 solar masses.
b. more than 3 solar masses.
c. between 0.4 and 1.4 solar masses.
d. less than 0.4 solar masses
e. not larger than the masses of the stars that we can see.
