On the way to school, a school bus driver stops the bus in front of a washroom and then he goes in. But the bus doesn't stop. After the driver gets off, the bus begins to run down the road, and there are 27 students on the bus. Luckily ,the 11-year-old student, David, goes to the driver's seat and begins to drive the school bus. He can't stop the bus, but he drives the bus away from a car. At last, he stops the bus near a shop and everyone is all right. A woman worker in the shop sees the whole thing. She says the bus nearly  runs into a river. We do not know how the boy stops the car. David is very quiet about the accident , but he is a hero. "If he doesn't drive the bus, all the students will go down into the river with the bus." says a teacher in the school. What is the passage mainly about?
A child plays in the street. A school bus driver. A bus runs into a river. A boy does something good.