口腔细菌分解残留在牙齿上的蔗糖、葡萄糖等，产生酸性物质，腐蚀牙釉质形成（）。

A.龋齿

B.牙周炎

C.牙髓炎

D.牙本质过敏

According to its content, a letter contains ______.

A. the purpose of writing the letter

B. supporting information
C. sender’s address



D. a routine remark