根据短文内容，选择正确答案。

   Mr Smith works in a factory in the middle of the city. The factory is not far from his home. It is about 800 meters away. So Mr Smith doesn't go to work by bus. He usually goes there by bike, sometimes he walks to work. It takes(花费) him 10 minutes to get there by bike or 20 minutes on foot. He usually leaves home at ten minutes to eight. Today something is wrong with his bike. He wants to walk there. His work starts at half past eight in the morning and finishes at a quarter(一刻钟) to five in the afternoon.