I'm not sure if you already use this method or not, but I'll just say it and I hope it helps. Here is the way I deal with long passages: I read the all of the first and last paragraphs and I only read the first sentence of each paragraph in between. Now, this might seems reckless, but trust me, it is really helpful and effective. Try it because even when the portion you're supposed to read to answer a question is not in the parts that you have read already, you'd still have line reference. This way, you make sure that you don't read things that are not mentioned in the questions (or things that have no questions based on). When you master this technique, you'd realize that it helps you avoid reading useless portions. Hope this helped! Goodluck!