The Early 1900s Was Pivotal for the Science of Genetics

The early 1900s was pivotal for the science of genetics because of which of the following events?

A) the rediscovery of Gregor Mendel's scientific discoveries
B) Thomas Hunt Morgan's identification of the first fruit-fly mutant
C) Walter Sutton's proposal that chromosomes contain genes
D) all of the above
E) None of these events occurred in the 1900s.