A teacher in a class of small kids asked them to categorize all the letters of the alphabet by a certain rule. Most students came up with the following correct answer which has three categories:
2. A, D, O, P, Q, R,
3. C, E, F, G, H, I, J, K, L, M, N, S, T, U, V, W, X, Y, Z
Can you guess what was the rule that the teacher had given?