The hard outer covering of an animal is a(n)

its depends on what animal like insects its a exo-skeleton  and a turtle or something alike a shell or some animals protect with bones

answer: - b cells

explanation: -

so, the b cells mediate their action by identifying the antigens present on the surface of the pathogens and then producing antibodies in return to mediate its effect.

lizards have adapted to life in the desert. some desert lizards have toes with spiny scales to them run across the sand without sinking. some use the sand to hide from predators, or to search for small animals that they prey upon.