Identify the sentence that uses incorrect parallel structure.

a. mom is watching tv in the living room, and dad is mowing the backyard.
b. strengthening core muscles, icing regularly, and visiting the chiropractor can all reduce back pain.
c. concerned citizens can write letters, show up at the polls, and will be wearing pins that say, "honesty now."
d. i usually like to unwind with a book or fall asleep in my beach chair.