At the end of BTTF III, when Marty arrives back to the real 1985 and picks up Jennifer, he encounters [the answer to Q9 in the BTTF II quiz], who then forces a drag race. Marty instead throws his truck in reverse and avoids colliding with THIS MAKE OF CAR, thereby not creating Marty's 2015 as seen in BTTF II (and, according to some, assuring the Cubs will never win the World Series).
Rolls Royce [As of this quiz's release, the Cubs are still in the hunt]