Given That White Dwarf Supernovae Are Such Good Standard Candles,why

Multiple Choice

Given that white dwarf supernovae are such good standard candles,why don't we use them to measure the distance to all galaxies?

A) They are rare events,so we have observed them in only a tiny fraction of all galaxies.
B) We cannot see them beyond a distance of about 100 million light-years.
C) They can occur only in spiral galaxies,not elliptical galaxies.
D) We would,but we don't have enough telescopes.