To discover whether bees can see colors, the following experiment is set up. A table is put in a garden, and on the table is a piece of blue cardboard (硬纸板) with a drop of syrup (糖浆) on it. After a short time, bees come to the syrup. The bees then fly to their hive (蜂窝) and give the syrup to other bees in the hive. Then they return to the feeding-place which they have discovered. After a while, the blue cardboard with the syrup on it is taken away. Instead of this card, a blue card is now put on the left side of the first feeding-place and a red card to its right. These now cards have no syrup on them. Thus, the blue card is on the left, the red card on the right, and there is nothing where the first blue feeding card used to be. Very soon bees arrive again, and fly straight to the blue card. None go to the red card.To do the experiment, altogether how many cards do you need to prepare？
A．Two, one blue and one red.B．Three, two blue and one red.C．Three, one blue and two red.D．Four, two blue and two red.

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