单项选择题

Once there was an old farmer, with a horse which was almost as old as himself. He set out one morning with his son to sell the horse before it died. Father and son walked, because the farmer did not want the horse to be too tired.
They met two men on the road. The two men said, "Why are you walking, farmer You have a horse. It’s a long way to the market." The farmer knew that was true, so he rode on the horse, while his son walked.
Then they met two ladies. "What are you doing up there, farmer Can’t you see how tired your boy is" So the farmer got down, and his son rode instead.
Next, three old men stopped them. One of them said, "Why are you walking, farmer Get up. It’s too hot for an old man like you to walk today." So the farmer got up behind his son on the horse, and they rode on.
Some time later, they saw a young woman. "Why aren’t you walking" she asked. "It isn’t far to the market. Give your poor old horse a rest." So the farmer and son got down once again.
Which of the following is wrong