短文改错 （共10小题，每题1分，满分10分）
假定英语课上老师要求同桌之间交换修改作文，请你修改你同桌写的以下作文。文中共有10处语言错误，每句中最多有两处。错误涉及一个单词的增加、删除或修改。
增加：在缺词处加一个漏词符号（∧ ），并在其下面写出该加的词。
删除：把多余的词用斜线（\）划掉。
修改：在错的词下划一横线（__），并在该词下面写出修改后的词。
注意：1.每处错误及修改均仅限一词;
2.只允许修改10处，多者（从第11处起）不计分。
Walter's goal in life was become a successfully doctor. He knew he had to finish high school first, so he puts his heart into his studies — in particular, biology, chemistry, or maths. Because he worked hard at these subjects, Walter became good at it. However, Walter forgot what he needed to master some other subjects besides those he had been chosen. As a result, Walter failed both English and Latin in the end of the second school year. But he had to repeat these subjects and he was almost unable to graduate like planned. Walter learned a good lesson.