Mrs. Black wants to visit her son. Her son works in a post office in the city ,but she doesn't know where it is , She begins to look for it , but she can't find it. She asks an old man, "Excuse me , how can I get to the post office?" "We have about forty post offices in the city," says the old man. "Which one do you want to go to ?" She gives her son's letter to him and the old man says , Walk along this street to the first crossroads and then turn left. You will see it on your left," She thanks the old man and soon finds her son . They are very happy. She can get to the post office by  _
walking along the street, and turning left at the first crossroads going straight along the street walking left at the corner walking along the street ,and turning right at the first crossroads