Solution:
The answer is (A). Let a,b,c be the number of turns in which, respectively, Annalisa, Bruna and Cecilia are in goal, while A,B,C are the number of turns in which they are on the field. If x is the total number of turns played, then we will have a=x−12, b=x−21, c=8 and A=12, B=21, C=x−8. At each turn, one of a,b,c increases by one, while two of A,B,C increase by one, so A+B+C=2(a+b+c) and substituting the previously found values gives x=25. Since a=13, there is only one way in which Annalisa could have played, namely if she starts in goal and returns there every two turns, thus never scoring a goal.