Mr Black is a careful driver. One day he is driving home. When he goes to a crossing, he sees a slow sign. So he slows down. He looks both ways. No car is coming, so he is ready to drive away.
Just then, he hears a police whistle (吹哨), so he stops by the side of the road. A policeman walks to him and says, "You should stop at the crossing." Mr Black says, "It's a slow sign, not a stop sign." The policeman looks at the sign and says, "Well, I am very sorry. I am in the wrong street."
