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作文,文中共有l0处语言错误．每处错误仅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l0处，多者(从第11处起)不计分．

Dear sir or Madame,

I’m Li Hua, a Chinese student take summer courses in your university. I’m writing to ask help. I came here last month and found my courses interesting. So I have some difficulty with note-taking and I have no idea of what to use the library. The learning Centre provided help for the students and I am anxiously to get help from you. I have not class on Tuesday mornings and Friday afternoons. Please let me to know which day is OK with you. You may email or phone me. Here is my email address and phone unmber:lihua@126.com, 12345678.

Looking forward your reply.

Yours,

Li Hua

嵌体预备时，错误的做法是（）

A.去尽病变腐质

B.轴面最大周径线降至龈缘

C.适当磨改异常的对颌牙

D.提供良好的固位形和抗力形

E.预防性扩展