A is for Alpha Centauri, whose human colonies were wiped out by the Xindi in the timeline of "Twilight"
B is for Bombing of the Earth Embassy on Vulcan
C is for Coalition of Planets, the proto-Federation beginning to form by series end.
D is for Denobula Triaxa, the home star system of the Denobulan race.
E is for T'Pol's Excellent bum.