题目

Many American presidents in the 19th century were born in poor families. They spent their childhood in little wooden rooms. They got little education. Washington and Lincoln, for example, never went to school and they taught themselves. Lincoln once did jobs for a worker, shop-keeper and post-master in his early years.     A large number of American presidents had experiences in the army. The two best known were Ulysses Grant and Dwight D. Eisenhower. Grant was a general in the American Civil War and Eisenhower was hero in the Second World War. It happened that they graduated from th18．圆的直径扩大3倍，半径扩大3倍，周长增加2倍，面积扩大9倍．