Innate immunity
1. utilizes highly specific antigen receptors on b cells.
2. is based on recognition of antigens that are specific to different pathogens.
3. is activated immediately upon infection.
4. depends on a newly infected animal's previous exposure to the same pathogen.
5. is found only in vertebrate animals.

3. is activated immediately upon infection.

Explanation:

Innate immunity is the nonspecific immunity. These immune defenses are present at birth and do not involve specific recognition of a microbe. Being nonspecific in nature, it acts against all microbes.  Innate immunity includes the first and second lines of defense.

Some of the examples of components of innate immunity among the first line of defenses are physical and chemical barriers of the skin and mucous membranes. Innate immune responses are the immunity’s early warning system that is generated immediately after the encounter with a pathogen to prevent them from entering the body and to help eliminate the ones that have entered the body.

Once a microbe has entered the body, secretion of antimicrobial substances and activities of natural killer cells, phagocytes, the process of inflammation, etc. serve to eliminate it from the body. All these responses are the components of innate immunity.

there's no big difference.

explanation:

the only little different between a rabbit and bunny is just that bunnies are much smaller than rabbits. bunnies are basically baby rabbits.