The End of the Life of a Red Dwarf Star

The end of the life of a red dwarf star is predicted to be a sphere of almost pure helium. But no such spheres have been detected. What do astronomers believe is the reason?

A) These helium stars are very dim and consequently hard to detect.
B) There are very few red dwarfs, so their end products are expected to be rare.
C) The evolution rate for red dwarfs is so slow that none has yet evolved to its end stage.
D) Helium is a relatively light material, so these helium spheres are expected to dissipate in a short time.