-How do you come here? You look tired(累的).     -________.

下列式子：x²，$\frac{1}{a}$+4，$\frac{3a{b}^2}{7}$，$\frac{2x}{\mathrm{\pi }}$，$\frac{ab}{c}$，﹣5x，0中，整式的个数是（　　）

   Danny is a schoolboy. He 1 in a small town. His home is about ten miles  2 school and the roads are not flat(平坦的). So it's 3 for him to get to school. He 4 at about five thirty every day and has breakfast. Then he5 school at around six o'clock. First, he6 his bicycle to the bus station. That takes about forty minutes.7 the bus takes him to school. It usually takes about thirty minutes. Sometimes he has8time for breakfast at home, so he has something for breakfast on the bus.
   “I've never taken trains. It must be a lot9fun than taking buses,” says Danny. He studies very10at school. He hopes he can go to school in a big city some day. He can take a train to school then.