"George has completely lost his sight during the past year but medical experts can find no physical reason for his blindness. This could be an example of"

Well if he hit his head hard enough then he could have damaged his sight in his eyes in the occipital lobe rather than the eyes them self.

answer; i believe that the correct answer is (decreased)

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."