Choose the sentence that is closest in the meaning...

Câu hỏi: Choose the sentence that is closest in the meaning to the root one.
I did not answer the door even though I knew it was my friend.

A. Unless I knew it was my friend, I would not answer the door.

B. I knew it was my friend, but I did not answer the door.

C. Only when I answered the door did I knew it was my friend.

D. I answered the door since I knew it was my friend.