Which of these statements concerning serfs in the feudal era is correct?
a. they had more rights than peasants.
b. many fought in service of their knights.
c. some saved enough money to move to other lands.
d. wealthy vassals often sold them to other vassals.

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 above statement is (true);