What might have been the first word out of Darwin's mouth at the end of his research travels?

A. Evolution.

B. Diversity.

C. Investigation. D. Selection.

All of these are associated with Darwin, but Diversity is a key to his thinking

D. selection

Explanation:

Through his travels, Darwin investigated how variety of species came to be and he worked on his theory of natural selection although at that time, it was referred to as selection where he theorised that certain survival traits selected for gave organisms an increased rate of survival, similar to artificial selection in pigeon breeding which was prominent back in the day.