C
Score, A C one; B D three; and one game. A plays alone.
First Trick.—B leads the ace of diamonds, D plays the ten, and A the knave.
Second Trick.—B leads the seven of diamonds, D trumps with the nine of clubs, and A plays the queen of diamonds.
Third Trick.—No matter what D leads, A is euchred.
B here makes the coup by recognizing what A must have for a trump-hand, and leads his small and losing diamond, making it imperative for his partner to ruff, thereby putting the lead through A, and establishing the euchre.