Most activities within a week can be made up except for: discussions assignments quizzes all of the above

This material looks like a question from a syllabus quiz; if this is the case, it is most likely particular to your teacher and we may not be able to provide the right answer. The most likely answer in my opinion would be quizzes, because many teachers will not allow you to make up quizzes, while assignments and discussions are probably going to be easier to make up. Hope this helps. 

In majority of classes, most activities within a week can be made up except for : Discussions.
Since you need another partner in order to do a  discussion, you can't just replace it if somehow you did not attend the actual discussion