Mr Smith works in a big city. Mrs Smith lives in a small town（镇）。Bill 是他们的儿子。 He is with his mother.
It's a Monday morning.Mrs Smith writes a litter（信） to Mr Smith.She says to Bill,"Go to the post office(邮局)with the letter and your father can get it on Friday. "Then Bill comes back late(回来晚).
"Why do you come back late?"
"There is a new post office in South Street（南街）.Do you know that?"
"Of course. It's far from our home. Why?"
"The letter is in the post office. "
"But there is a post office near our home. "
"I know,but the post office in South Street is near Dad. He can get the letter earlier(更早地). "
