Whether or not you are a native English speaker, try to find a reading methodology that helps you absorb. Make sure you are really taking in the meaning of those sentences you are going through. That you are not, for example, skimming details which may turn out to be important later on. In some ways, Reading Comprehension on the GMAT means exactly that - Do you actually "comprehend" what you are reading? A litmus test you can use to see if you have absorbed a passage well is whether you can speak about the passage after going through it. If you can't find a good methodology to use, perhaps ask someone who does well on RC what they do. The one I teach to students (native and non-native English speakers alike) doesn't necessarily rely on note-taking per se but perhaps you find doing so helps. Making a few illustrations "imagery" can be helpful too sometimes depending on what is being discussed.
You don't need to waste passages from the Official Guides to work on your reading. Consider practicing on any articles similar to them. Even if you do decently on RC already, one of the potential benefits of improving your absorption is not having to go back and forth between the answer choices and the passage as much.
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