Question: Five hundred flies of one species were sprayed with a new insecticide. Twenty-four hours later, nearly all the flies were dead. However, a few survived. Which principle best explains why some flies survived?

  Options: 
 A. Animals adapt to new environments.
 B. New species develop from survivors.
 C. There is variation among individuals within a species.
 D. Insecticides may cause genetic mutations.
Answer: C