Thomas Hunt Morgan's Choice of Drosophila Melanogaster Has Been Proven

Multiple Choice

Thomas Hunt Morgan's choice of Drosophila melanogaster has been proven to be useful even today. Which of the following has/have continued to make it a most useful species?
I.its four pairs of chromosomes
II.a very large number of visible as well as biochemically mutant phenotypes
III.easy and inexpensive maintenance
IV.short generation time and large number of offspring

A) I and IV only
B) II and III only
C) I, II, and III only
D) II, III, and IV only
E) I, II, III, IV, and V