I must apologize to you as I opened your letter in ________ yesterday.

I must apologize to you as I opened your letter in ________ yesterday.

A.mistake

B.fault

C.error

D.crime

答案及解析： C

解析：

题意：我必须向你道歉，因为我昨天误拆了你的信。in error为固定搭配，意为"错误地"，其他三项无此用法。