OK, fools leap in where angels fear to tread ...
I am afraid that the more I have looked at this question, the less I like it. Firstly, it uses the concept of "cannot be true", rather than "must be true" which I not aware has appeared in any other sets of papers. Secondly, it requires specific general knowledge, something that the 11+ is not designed to test.
That knowledge is of the way that a football knockout tournament is organised (and mine can be written on a postage stamp, so others should feel free to disagree with me).
If each school played every other school, that amounted to 20 games. There would therefore presumably have to be at least one further match to determine the winner, and therefore there had to be more than 20 games.
However, there is nothing to say how the tournament was won. If, for example, it was decided on Won/ Lost/ Goal Aggregate, and one school was already victorious without the need for a final, then statements A and D would both
Maybe I'm missing something though - the mere mention of footie does strange things to my brain.