Back to the Future or Harry Potter and the Half-Blood Prince?

Are you a fan of Harry Potter and the Half-Blood Prince? Of Back to the Future as well? Prove it! Select which quote belongs to which movie and see how good you are:

- Why is it, when something happens, it is always you three?

- Believe me, Professor. I've been asking myself the same question for six years.

- 1.21 gigawatts! 1.21 gigawatts. Great Scott!

- What-what the hell is a gigawatt?

- Hey! She's only interested in you because she thinks you're the Chosen One.

- But I am the Chosen One... Sorry... kidding!

If my calculations are correct, when this baby hits 88 miles per hour... you're gonna see some serious shit.

- We better back up. We don't have enough road to get up to 88.

- Roads? Where we're going, we don't need roads.

- Has it ever crossed your brilliant mind that I don't want to do this anymore?

- Whether it has or it hasn't is irrelevant; you gave me your word.