Darwin's Ideas on Evolution Were Based on a Number of Observations

Darwin's ideas on evolution were based on a number of observations. Among the most important observation was that

A) all the types of organisms that have lived on Earth are present today.
B) individuals within a population are all virtually identical to each other.
C) there is usually ample food and water for all populations.
D) when natural resources become scarce, competition occurs between members of the same species.
E) populations will only produce as many offspring as can be accommodated by the environment.