Back to the Future was a massive surprise hit in 1985. So much so that the studio had no choice but to make a few more - and to work with the open-ended final scene they set themselves up with in the first one. Back to the Future Part II does raise some questions. Like why does everyone’s descendants look exactly like them? Why bring Jennifer along at all if Doc just wanted to knock her out? How does Biff know how to operate a time machine? (thetvdb.com)