15. Amy, Bob, Cat and Dee occupy the top four positions in a chess tournament. The sum of Amy's position, Bob's position and Dee's position is 6 . The sum of Bob's position and Cat's position is 6 . Bob finished ahead of Amy. Who came first in the tournament?
A Amy
B Bob
C Cat
D Dee
E You can't be certain
15. D Since $1+2+3+4=10$ and the sum of Amy's position, Bob's position and Dee's position is 6, Cat came fourth. Hence, since the sum of Bob's position and Cat's position is also 6, Bob came second. Therefore, since Bob finished ahead of Amy, Amy finished third. Therefore Dee came first in the tournament.