And, if you did PT50 (Sept 2006), you haven't even gotten to the Comparative Passages era of LR. Another major shift; IMO, one for the better (I have the least problems on Comparative Passages, but others have different experiences).
For Q5 I think "mainstream" is meant to be considered "watched by most". So a reason to show political talk shows that are bland etc (the overall conclusion) you must assume that this is what most tv watchers want to watch.
Remember G3-->Q5, but Q is clearly in 4, so that negates the necessary condition, triggering a negation of the sufficient condition. In other words, G cannot be in 3. That leaves only J and H for slot 3. Hence, answer D
Something that helps me is circling words that I think would be really hard if they ask about them, because they tend to ask about those parts. One RC passage from the PT50's had 3 questions about one extremely confusing sentence in the passage.