Whoa... they really cleaned this place up. Looks brand-new. No...
[Marty sees the outside of the Hill Valley High School in 1955]
Marty McFly: Whoa... they really cleaned this place up. Looks brand-new.
[Marty and Doc walk toward the building]
Dr. Emmett Brown: Now, remember - according to my theory, you interfered with your parents first meeting. If they don't meet, they won't fall in love, they won't get married and they won't have kids. That's why your older brother's disappearing from that photograph. Your sister will follow, and unless you repair the damage, you'll be next.
Marty McFly: Sounds pretty heavy.
Dr. Emmett Brown: Weight has nothing to do with it.