The correct answer is C: remind them to watch the lecture again.
If somebody asks you to give them your homework to copy you should always refuse. Copying homework is bad on many levels and you can be severely punished for doing so. It is also considered cheating and misusing somebody's trust.
Instead, the person who asked you to copy your homework should try to solve the assignment himself. In order to do so, he should watch the lecture again and concentrate, trying to understand the content, so that he would not feel the need to copy from others.