Which type of insurgent approach involves a few leaders and a militant cadre or activist party seizing control of government structures or exploiting a revolutionary situation?

you should think about the answers you give and expect the same form your questions.

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."