A、Because he lost one. B、Because he only bought three. C、Because he forgot to count the one he was riding. D、Because he didn’t k

One day a farmer bought four donkeys at the marketplace in the village. He got on the back of one of them and began to ride home.
    As he was riding along, he noticed that there were only three donkeys walking in front of him. He expected to see four. "I wonder what happened," he said to himself. "I bought and paid for four donkeys, but now it appears that I have only three. "He was forgetting, of course, to count the donkey he was riding on.
    When he got home, his wife met him in front of their house. "I see that you bought four donkeys," she said, "Did you buy them for a good price?"
    "Yes, I did," he said. "but something puzzles me. I bought four donkeys at the marketplace this morning. And I am sure that I had all four with me when I left the village. But now it seems that I have only three." "See?" He even counted them, "One, two, three." He still didn’t remember that he was sitting on the back of one of the donkeys at that very moment.
    At first his wife stared at him, waiting for him to smile, for she thought he was joking. Then when she noticed that he was not, she turned away and laughed. "How strange," she said. "You see only three donkeys but I see five!"