短文改错（共10小题，每小题1分，满分10分）

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：在缺词处加一个漏字符号（∧），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，并在其下面写出修改后的词。

注意：1.每处错误及其修改均仅限一词；

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 put his heart into her studies----in particular, biology, chemistry and maths. Because he worked hard at these subjects, Walter became good at it. However, Walter forgot that he needed to master some other subjects beside those he had been chosen. As a result, Walter fails in both English and Chinese 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.

流体在管中稳定流动时的流速与管内径的关系是（）

A.与管内径成正比

B.与管内径的平方成正比

C.与管内径的平方成反比

D.与管内径成反比。