7. Six people (two wearing green shirts, two wearing pink shirts, two wearing gray shirts) want to divide themselves into three teams of two people each to play briscola. In how many ways can they make the division so that the two in each team have shirts of different colors?
(A) 4
(B) 11
(C) 8
(D) 24
(E) 15
Problem 7. The answer is (C).

The two people with green jerseys cannot be on the same team; furthermore, their teammates must have jerseys of different colors, otherwise, in the remaining team, there would end up being two people with jerseys of the same color. One green player is therefore paired with a pink player, while the other green player is paired with a gray player. The composition of these two pairs also determines the third. We have two possible choices for the green player who plays with a pink one; the other green player will team up with a gray one. At this point, we have two choices for which pink player plays with the first green and which gray player plays with the second green. All choices are independent, and we therefore have a total of $2 \cdot 2 \cdot 2=8$ ways to pair the players.

(Problem proposed by A. Bianchi)