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：把多余的的词用斜线（＼）划掉。

修改：在错的词下面划一横线，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。

    Today we had a chemistry test. I found the test difficulty, but I tried hardly to do it. Suddenly, my best friend Mary asking me to let her to copy my answers. After think for some time, I let her copy my answers. But after the test, all of us were called to the teacher’s office. The teacher was angry because we had same answers in the tests. We were warned not to cheat again so she would need to see our parents. I was very upset. I was just helping a friend. Why does she punish me?

已知圆内接正三角形的边心距为2cm，求它的边长．

下列正确的是（   ）