Since we don't know the dora tile, I would discard either circle 6 or circle 8. Circle 6 is of course the "right" answer but since circle 9s already form a pair I don't see any harm in discarding the circle 8.

As for newcomers looking at this guide I have this to say; just play the game, observe your replays and write down stuff that you notice. I taught myself how and when to fold, how dragons and wind and 1-9 tiles have priority, how a discarded number 3 tile makes discarding number 1 and 2 tiles safe against chi or number 6 tile less risky and a whole lot else.

Do what you can on your own and when you feel like you are reaching a bottleneck, then look up the theories and mix it with what you have learnt.

The answer is A. 6p. The five-block method divides the hand to 1m1m1m, 6m7m7m, 3p4p, 6p8p9p9p, 4s5s, which makes 6p a redundant tile.

In addition, it is not recommended to use the six-block method to discard 7m because the hand would lose the shape to accept 7m and 9p which will increase the value of this hand.