下列句中划线字的活用与其他三句不同的一项是（   ）

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：在错的词下面画一横线，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。

Dear Mike,

    How happy we are to know you're going to participate in our Chinese Idiom Contest. Here are what you are supposed to know about.

    The contest will be hold in the school library at 8:00 a.m in July 15, 2018. Characters wrong used should be recognized in some Chinese idioms. Besides, you are required say out the idioms by guess gestures of your partner. Hopefully, why I have to remind you of is that you'd better to get one story idiom prepared in case you are probably invited to tell one. By the way, all our Chinese teachers will be invited as judge.

    Expect your excellence performance in the approaching contest.

    Best wishes!

Yours,

Li Hua

求证：三角形的中位线平行于三角形的第三边，且等于第三边的一半．