Pop Quiz, Hot Shot!

(I'm studying for the NY State Bar, so I tend to think in multiple choice questions these days)

Since Barack Obama officially locked up his party's nomination, John McCain has been challenging him to a series of joint appearances at town halls, where the two can debate in a more informal setting.

John McCain is doing this because:

(a) The difference between this and this.

(b) Alone, he can barely fill a high school gym.

(c) McCain has loved this style of forum since watching the Lincoln/ Douglass Debates as a young boy.

(d) The Rule Against Perpetuities.