The End Product of a Red Dwarf Is Believed to Be

The end product of a red dwarf is believed to be a star of pure helium. How do we know this?

A) We are watching the evolution of red dwarfs in our galaxy. Some of those are very near the end of their main-sequence life cycle, and they are essentially pure helium.
B) There are many pure helium stars in our galaxy, and these are presumed to come from red dwarfs.
C) There are no pure helium stars around, but there are later generations of stars that must have evolved from stars of pure helium.
D) The lifetimes of red dwarfs are too long for any of them to have completed their evolution, but we have theoretical models.