Bats carry a large number of viruses, which can cause fatal danger to humans and other animals, but bats seem to be unaffected by these viruses. Why? Scientists think this may be related to bats being the only mammals that can fly. During the evolution of adaptation to flight for hundreds of millions of years, many of their systems have changed, including the defense and immune system. Generally speaking, the immune response of the human and other animal bodies helps the body to resist the virus, but the Excessive immune response may cause serious diseases, and the bat's immune system can just reach a balance in the process of symbiosis with the virus. In the following inference, the correct one is. ['Bat is one of the oldest mammal species, with hundreds of millions of years of evolution to date.', "The bat's body's immune system resists virus attacks without triggering an overly strong immune response.", 'As an ancient creature, bats have evolved super genes that can defend against various viruses.', 'Bats can fly is the most important reason for their wide spread of deadly viruses on a large scale.']