Innate immunity . is found only in vertebrates is the first, and most general, mechanism of protection against pathogens depends on an infected animal's previous exposure to a pathogen is based on recognition of antigens that are specific to a pathogen

is the first, and most general, mechanism of protection against pathogens

Explanation:

Innate or natural immunity is one of the two types of immunity an organism can possess (the other being; acquired immunity). Innate immunity is the FIRST defensive response of an organism against pathogenic attacks. The acquired immune system is only activated when the innate immune system has been penetrated or surmounted.

For example, the skin, mucus secretion, inflammation etc. are all natural or innate defenses against foreign invaders. Therefore, according to this question, innate immunity the first, and most general i.e. commonly used, mechanism of protection against pathogens.

when atoms of different types of elements join together, they make molecules called compounds. water consists of compound molecules made up of 2 hydrogen atoms and 1 oxygen atom. this is why it's called h2o. water will always have 2 times the number of hydrogen atoms as oxygen atoms.