I hope you will forgive me___opening your letter__mistake.A.

題目：

I hope you will forgive me___opening your letter__mistake.A.for;for B.of;for C.for;by D.of;by
I hope you will forgive me___opening your letter__mistake.
A.for;for B.of;for C.for;by D.of;by
正確的應該算哪個?還有這個句子中出現了哪些知識點?

解答：

C
for 表示原因
by mistake 固定詞組, 弄錯的意思