1. Five hundred cockroaches of one species were sprayed with a new insecticide. Twenty-four hours
later nearly all the cockroaches were dead. A few, however, survived. This outcome illustrates which one
of Darwin's key ideas about natural selection and variation?
A. All living things come from preexisting living things
B. Animals adapt to new environments.
C. There is variation among individuals within a species.
D. New species develop from survivors.

C. There is variation among individuals within a species.

Explanation:

According to the conditions mentioned in the question, some cockroaches survived even in the presence of insecticide. This is mainly due to the genetic variations they had within a species. These variations are mainly due to crossing over which the members of the same species develop during breeding. It is important to consider that these variations are often single nucleotide polymorphisms (SNPs). The higher SNP rate allows the organism to be diverse in challenging environmental conditions. Therefore, the survived cockroaches might have these variations that helped them survive even in the presence of insecticide.