Mr p, Mr q and Mr s are invited to guess a poker. There are A.4.7.9 hearts, J.8.4.2.7.3 spades and K.Q.5.6 diamonds in the pile. Professor A.5 got 16 cards from this pile of cards.

Solution: it is to gradually select uniqueness from known conditions.

The first sentence: P doesn't know which card it is, so the points in his hand are determined to be AQ45, because the points of other cards are unique, and P knows the points when he holds them.

The second sentence: Q knows that P doesn't know which card it is, so it can be determined that the suit is hearts and diamonds, because only these two cards have no unique cards.

In the third sentence, P knows what card it is, so it removes A, because among the two colors of hearts and diamonds, only A is not unique. If P holds A, it cannot be judged.

The fourth sentence: Q also knows what P is, so lock that card to 5 diamonds. Because there are two hearts, if the suit in Q's hand is a heart, it is impossible to determine its uniqueness.

To sum up, the answer is cube 5.