Read the passage.
Passage(1)The effect of sleep deprivation on your test-taking ability depends on the type of exam questions. (2)If they're multiple choice or true/false questions, a night without sleep won't affect your ability to deal with them. (3)The reason is that in answering such questions you rely on familiar, established problem-solving techniques. (4)Such techniques are unaffected by the loss of one night's sleep. (5)If, however, your exam included essay questions, you'd be in trouble. (6)To answer this type of question, you need to think flexibly. (7)And this ability is diminished after only a single sleepless night.
The relationship of sentence 5 to sentences 2-4 is one of
a. Addition.
b. Time.
c. Contrast.
d. Illustration.