The major function of the immune system is to protect the host from environmental agents such as microbes or chemicals, thereby preserving the integrity of the body. This is done by the recognition of self and response to non-self.
Answer:
A- Different species
Explanation:
Dogs and Cats are distinct species incapable of producing offspring because of the many differences in their genome.
I belive its called a metric system
By the process of cell differentation
