Choices: 1. desire; 2. sound; 3. saliva; 4. humans; 5. Light; 6. DNA; 7. zoos; 8. gametes;
Given those answer options, answer the question: Fact 1: Sound can be used for communication by animals. Fact 2: For mating, communication is between individuals of the same organism. Given the two facts above, what do animals use to find a mate?
A:
2.