unfortunately, those questions don't all fit neatly into a particular box. you have to use transition words (such as "however", "therefore", "even though", and the like), and, additionally, there's no real way around what i'm going to say next: you have to
understand the argument.
among all cr questions, these are probably the ones on which you will get the least mileage by just using strictly memorized techniques (as opposed to certain other genres, such as "draw the conclusion", on which you can get most of them by following a memorized set of rules).
here's a thread on another forum, on which i analyzed one of these problems in a certain amount of detail (you'll have to scroll back to the beginning):
http://www.beatthegmat.com/endorphins-t ... tml#244744