Q: Fact 1: Thirst is used to make an animal realize that it needs to replenish its bodily water by the body. Fact 2: Every body needs plenty of hydration, and water is the best source of that hydration. Given the two facts above, what is used by animals to realize their bodies need hydration?

Available choices:
(1). shelter;
(2). keratin;
(3). fever;
(4). excretory;
(5). Enzymes;
(6). thirst;
(7). food;
(8). sores;
The answer is:
(6).