In repeated exposure to the same microbe, the subsequent (secondary) responses of the innate immune system are generally described a?

The primary and secondary responses are equal

Explanation:

Primary and secondary are considered to be two responses of immune to the antigen.  

Primary response occurs at the first encounter between the antigen and immune. This response can be as long as 14 days depending on the antigen category.

There are two cells in the body that act as a defensive system and antibodies against antibodies.

the secondary response occurs when a person exposed to the same antigen repeatedly

d. i assume the underlined word is "role." reformat if it isn't.

explanation:

role is closest to part because when replacing words, "playing a vital decision," "playing a vital activity," and "playing a vital dollar" don't make logical sense. the only meaningful choice is "playing a vital part."

this fits one of merriam-webster's definitions of role: "a function or part performed especially in a particular operation or process."