小明想了解自己一学期数学成绩的变化趋势，应选用____ 统计图来描述数据．

    It was a hot summer day that found me running down the street with a dollar in my sweaty hand. The closer I got to Sam & Joe's Stationery Store, the more excited I was. After all, a dollar was a tidy sum for an 11-year-old boy in 1961.

    Out of breath, I swung open the door and got a blast of cold air that instantly cooled me off. I was in a place of pure happiness. Sam & Joe's had it all—books, candy, toys, baseball cards，puzzles and games. I went directly to the bar and ordered a bottle of soda. There I sat, considering my next move.

    Books always came first. I picked out five titles. Next came the candy, rows and rows of it. I chose five candy bars, which brought my total to 75 cents. Then a bottle of cold orange juice, a bag of chips and a pack of Ted Williams baseball cards. After paying the clerk, I still had 5 cents.

    I hurried directly to my backyard, where an apple tree patiently waited for me. There, sitting in the shade against its strong trunk, I read my books, ate my candy and drank my orange juice.

    As I sat in my own personal heaven, I started thinking about having more. That's when a fantastic life—changing idea popped into head: If I could get more money, I could buy more books I liked, buy anything I wanted. That's how it all started.