Thanks for weighing in, Drew
The "everything is underlined" and "big chunks of the sentence move around" questions are very difficult, yes.
You have gotten used to scanning for single word or maybe 2-word changes. That's good. Now, you need to expand that skill to entire phrases or clauses. Maybe an opening modifier is picked up and moved to the end of the sentence. Why? How does the placement of the modifier affect things? Noun modifiers are supposed to be next to what they modify, so that might give you one clue about what to examine.
In even harder ones, they may change around the roles of different parts of the sentence - a modifier may become the main clause and the main clause may become the modifier, for example. This only happens typically on the hardest questions, so what you do depends a bit on your goal. If you're not looking for a super-high verbal score, then maybe you don't care if they give you a couple of these - you just make sure that you guess before spending too much time.
If you are looking for a super-high verbal score, then you're going to have to learn how to break the sentence down into its component grammatical parts. We also have a workshop called the SC Slam (Quest for 750), and it teaches this Core / Modifier technique that I'm talking about.
First, as a general rule, this article discusses how to move through any SC problem:
http://www.beatthegmat.com/mba/2010/06/ ... on-problemNote that scanning vertically (as discussed in the article) may require comparing big chunks of sentences, as I mentioned above, rather than just single words.
Next, I don't have an article that covers one of these "everything is underlined and moving around" problems, but I'll tell you what: I'll go find one in GMATPrep and write my next article about it, okay?
My next open publication date is 8 March (sorry it's so far out - that's what a publishing calendar is like!). Check the home page of
http://www.beatthegmat.com on that day and you'll see the article. In the meantime, try to do it on your own, using what I talked about above (looking at phrases and clauses, not just individual words).