Which is the best example of a public good? *

A public good is an example of a good or product that individuals can consume or use without reducing its total availability for others. Goods like national security, sewer systems, public parks, among others, are considered as public goods.

Explanation:

Hope this helps :)

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."