Why this constitutions is called a
federal democratic republic constitution

The Constitution established a Federal democratic republic. It is the system of the Federal Government; it is democratic because the people govern themselves; and it is a republic because the Government's power is derived from its people. ... Separation of powers, or branches of Government with separate powers.

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; make a no-nonsense accusation of the other;