One day after school, I went to the teacher's office to see my teacher, but nobody was there. As I was about to leave, I noticed a piece of paper on the floor. I picked it up and saw the words "FINAL-TERM EXAMINATION" at the top. I put the paper into my school bag secretly and ran out of the room. After I came back home, I took out the paper quickly. It was the exam paper of my worst subject, History. I felt excited. My heart beat fast. I took out my History book and started working on the answer. I had never answered any questions so seriously. On the day of the History exam, I went into the exam hall confidently. When the paper was sent to me, I dreamt of getting the highest mark in the whole grade and could not help smiling. "My History teacher always encouraged me to work hard and get better grades, but I let him down time and time again. This time I will give him a big surprise," I thought. When  the  teacher  said  we could  start,  I turned  the  paper  over. To my surprise,  all  the questions were different. Later I felt nervous. In the end, I almost left the paper undone. After the exam. I ran to the toilet, took out the paper and carefully read it from the top. Oh! It was last year's exam paper. I read all the questions but I hadn't read the date. This is a lesson in which I know I have to put my feet on the ground. I regretted doing such a silly thing. After that, I told my teacher the truth and I promised to be honest. From then on, I worked harder than ever before. When did the writer know it was last year's exam paper?
Before he read all the questions. As soon as he returned home. Until he went into the teacher's office. After he read the paper in the toilet.