You are in possesion of a card set. On one side there is a shape, a circle or a triangle. On the other side there is a colour, blue or yellow. There is one rule: If there is a circle on one side of a card, then the other side is blue. You have four cards placed on a surface next to each other, one depicting a circle, one a triangle, one is blue and one is yellow.Which card or cards do you need to turn around in order to confirm the abovementioned rule?