Why are yeast cells often used to study eukaryotic gene mutations affecting secretion and other cytomembrane processes?

A)They have only a few genes.
B)They are small and single-celled and can be cultured easily.
C)They can be grown as haploid organisms so mutants are easily seen.
D)Deficiencies in yeast cells caused by mutants are easily detected.
E)All of these are correct.