题目

Zhang Hua now lives in a big city with his parents in Shangdon. He lives near an underground station (地铁站), so sometimes he can take the underground to some places. There is a big museum in the middle of the city. Zhang Hua often visits it with his father on weekends. There he can know a lot about science. Opposite the museum, there is a bookstore. Every time he goes out of the museum, he always goes into the bookstore and buys some books. A post office is 500 meters away from his house. He often goes there and sends some letters for his father on foot. On the way to the post office, he I was so familiar with her that I recognized her voice _____I picked up the phone. A. the moment  B. after  C. before D. while