The federalist papers were written to

The Federalist Papers were written to explain and defend the newly proposed U.S. Constitution and gain support for its ratification.

Explanation:

The Federalist Papers were a series of 85 essays written by Alexander Hamilton, James Madison, and John Jay and published in 1787, to explain and defend the newly proposed U.S. Constitution and gain support for its ratification.

In these papers, the authors addressed constitutional principles, explained the deficiencies of the Articles of Confederation, gave details of the new proposed Constitution, and argued why its ratification would preserve the Union and empower the federal government to act firmly and coherently in the national interest.

well to answer ur question to be completly honest

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."