C. pursue
(All other words have the stress on the first syllable, while "pursue" has stress on the second syllable.)

D. participate
(The stress on "participate" is on the second syllable, while the others are stressed on the first syllable.)

B. machine
(All other words are stressed on the first syllable, while "machine" is stressed on the second syllable.)

D. unpleasant
(All other words are stressed on the first syllable, while "unpleasant" is stressed on the second syllable.)

B. interest
(All other words are stressed on the first syllable, while "interest" has stress on the first syllable in noun form, but stress changes in verb form.)