As one comes to some crossroads, he or she sees a sign which says that drivers have to stop when they come to the main road ahead. At other crossroads, drivers have to go slow, but they do not actually have to stop unless, of course, there is something coming along the main road; and at still others, they do not have either to stop or to go slow, because they are themselves on the main road.
Mr. Williams, who was always a very careful driver, was driving home from work one evening when he came to a crossroad. It had a “SLOW” sign. He slowed down when he came to the main road, looked both ways to see that nothing was coming, and then drove across without stopping completely.
At once he heard a police whistle, so he pulled into the side of the road and stopped. A policeman walked over to him with a notebook and a pen in his hand and said, “You didn’t stop at that crossing.”
“But the sign there doesn't say ‘STOP’.” answered Mr. Williams, “It just says ‘SLOW’, and I did go slow.”
The policeman looked around him, and a look of surprise came over his face. Then he put his notebook and pen away, scratched his head and said, “Well, I’m in the wrong street!”
When he was stopped by a policeman, he ____.

A．was driving at a high speed	B．was driving onto the main road
C．was going to stop his car	D．was pulled into the crossroad

Though slowly, Mr. Williams continued driving at the crossing because________ .

A．he saw a “STOP” sign in the opposite street

B．he paid no attention to the traffic rules

C．he didn't have to stop

D．he was eager to get home

Looking round Mr. Williams, the policeman was surprised because__________ .

A．he met a mad man

B．he realized that he himself was mistaken

C．Mr. Williams dared to speak to him like that

D．Mr. Williams would not apologize to him

What does “scratch” in the last paragraph mean?

A．to rub the skin of (the head) for uncertainty

B．to strike (the head ) for regret

C．to nodded for sure

D．to look back to search for something