阅读理解，根据材料内容选择最佳答案。
Last Friday. I agreed to meet some friends at 6：00 pm in a coffee shop. The weather was sunny, so I decided to walk there. I arrived ten minutes early. I ordered(点) a cup of coffee and sat watching people. There were some boys playing football on the street, and a small boy was running after the ball as it rolled(滚) across the road.
Suddenly, there came a car. It was going very fast. When the driver saw the boy in his way, he braked (刹车) hard. But it was too late…The small boy was lying on the street without moving. To everyone's surprise, the car didn't stop. It drove away quickly.
People ran to the boy. There was a cut on the boy's head and he lost a lot of blood(血). The coffee shop owner(主人) telephoned the police. Soon an ambulance (救护车) arrived and took the boy to the hospital.
At 6：30 pm, the police arrived and started questioning people. About half an hour later, they asked me to go to the police station because I saw everything. I gave them all the information I knew because I really wanted them to catch the driver. I didn't leave the police station until 8：00 pm. After that l went home because I didn't want to talk to anyone.
The next day, the boy's parents called me to say thanks. They also told me their boy was fine and the driver was at the police station now.
的公比为正数，且
·
=2
，
=1，则
=
