What are players’ strategies?

A、player 1’s strategies are: a, b; player 2’s strategies are x, y
B、player 1’s strategies are: aa, ab, ba, bb; player 2’s strategies are x, y
C、Player 1’s strategies are: a, b; player 2’s strategies are xx, xy, yx, yy
D、player 1’s strategies are: aa, ab, ba, bb; player 2’s strategies are xx, xy, yx, yy