Which Element of Darwin's Theory of Evolution Had Been Discussed

Which element of Darwin's theory of evolution had been discussed among scientists for more than a century before?

A) Life on Earth had been changing and developing for millions of years.
B) Some species are more successful than others in adapting to changes in the environment.
C) Individuals who survive will pass on their attributes to the next generation.
D) Chance variations give some organisms an advantage over others.
E) Genetic mutations can allow some individuals to become dominant.