英语短文改错题,

英语短文改错题,
请帮做下,最好能有解析,
Mark is a middle school student.He lived in the middle of the town.About a mile from Mark's building,there have many old houses.They are all empty and going to be pulling down.His father says they are dangerous and tells him to keep away from them.But he enjoys playing here very much.One Friday on their way home from school,Mark went into one of the empty old houses.He saw a door leading a small dark room.He went into the room to see what he could find them.Just then he heard a terrible sound.The roof of the old house fell off.Mark tired to open a door.However,he couldn't.But he had to stay there.Mark was saved three days late by some policeman.They used dogs to find him.