Mr. velasquez is participating in a clinical research study that is investigating psychological factors that may influence the development of heart disease. when he is instructed to imagine a situation in which he was very angry, the sensors monitoring his heart reveal that

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; all over the above; //everybody