Given a scientific question and its correct answer, generate supporting facts for the answer. This supporting fact can be an explanation for the answer to the given question.

[Q]: Question: What type of mammals are humans? Answer: placental mammals
[A]: Human beings are mammals. Like other mammals, we have hair and mammary glands. The subclass in which the human species is classified is the placental mammals.

[Q]: Question: What are interferons? Answer: cytokines
[A]: Figure 42.4 Interferons are cytokines that are released by a cell infected with a virus. Response of neighboring cells to interferon helps stem the infection.

[Q]: Question: What kind of relationship exists between living things that depend on the same resources? Answer: competition
[A]:
Competition is a relationship between living things that depend on the same resources.