Nearly all galaxies contain Cepheid variable stars. Why, then, do we determine the most distant…

Nearly all galaxies contain Cepheid variable stars. Why, then, do we determine the most distant galaxy distances using white dwarf supernovae rather than Cepheids as standard candles?
      
a. White dwarf supernovae can be detected with a single observation, while it takes many observations to measure a Cepheid's light curve.
      
b. White dwarf supernovae are much more reliable standard candles than Cepheids.
      
c. White dwarf supernovae can be observed in galaxies that are too far away for us to see individual Cepheids.
      
d. White dwarf supernovae are more common than Cepheids.