阅读理解。 Mrs. White has a son. His name is Sam White. The young man works in a post office in a city. He asks his mother to visit the city, and the old woman is happy and catches (赶上) a train. Soon she gets to the city, but she doesn't know where the post office is. She begins to look for it. but she can't find it. At a bus stop she asks all old mall, 'Excuse me, sir, how can I get to the post office?' 'We have about forty post offices in our city,' says the old man.'Which one do you want to go?' The old woman gives Sam's letter to him and the old man says,'Walk along this street and take the fourth turning on the left. His post office is just there.' Mrs. White thanks the old man and soon finds her son. They're very happy. A week later the woman goes to the zoo. She sees all kinds of animals but after that she can't find the way to the post office again. At the same bus stop she meets the same old man and she asks the same question again. 'Oh dear!' the old man calls out.'Are you still looking for your son?' 根据短文内容， 回答下列问题。 1. Where does Sam White work? ____________________________________________________________________________ 2. How does Mrs. White go to the city? ____________________________________________________________________________ 3. Does the old woman know how to get to her son's post office? ____________________________________________________________________________ 4. How many post offices are there in this city? ____________________________________________________________________________ 5. Does the old man know Mrs. White finds her son? ____________________________________________________________________________