President Barack Obama was criticized by opponents for usurping congressional powers when he did which of the following? President Obama signed a treaty regarding Iran’s use of nuclear power.

President Obama issued an executive order protecting some undocumented immigrants.

President Obama proposed and advocated an expansive healthcare program.

President Obama ordered a covert mission to find and kill osama bin laden.

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."

answer; the sons of liberty;