I just wanted to clarify a few points in your question, because at the moment only the answer given to part C seems reasonable to me. This leads me to think that you may have rephrased the question, rather than posting in its original form. Are you told the size of the group of teenagers that you are selecting from? The question says "4 out of 5", but presumably that is saying "80% of teenagers", rather than "in a group of 5 teenagers, 4 have a wireless device", as in this latter case, part A would make no sense. I may have some more questions for you depending on your response.