The Main Sequence Has a Limit at the Lower End

Multiple Choice

The main sequence has a limit at the lower end because

A) low mass stars form from the interstellar medium very rarely.
B) hydrogen fusion combined 4 hydrogen nuclei to form 1 helium nucleus.
C) pressure does not depend on temperature in degenerate matter.
D) the lower limit represents when the radius of the star would be zero.
E) there is a minimum temperature for hydrogen fusion.