In problem 1, what is the ``membership'' of a team?
Answer: This question was designed by a soccer fanatic, so I'm guessing that it is the league in which the team participates. Apparently this is a big deal in European soccer, where teams are moved to better or worse leagues, depending on how they did the previous year.
What is ``mixing''? What is a ``version'' of a song?
Answer: Actually, it doesn't matter. All you need to know is given by the ODL in Problem 2. Songs are mixed by DJ's, and versions is a symmetric relation on songs. I would imagine that two songs are versions of each other if they have the same basic melody and words. The process of mixing is a combining of electronic signals, usually from instruments or microphones. Perhaps someone who is more into music than I am can give me more details, which I will post here. But again, you can answer the questions without understanding the underlying electronics.