Task: Question Answering
Input (English): 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?  
 (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.
Output (English): C