it concerns me that you mention not having a clear grasp of the passage - the use of the term "shaky".
it is difficult to answer any of the questions without a clear understanding of the passage. this - including structural understanding - should be your main goal when reading
. we don't really read passages ----> we analyze them, pick them apart.
when i say clear understanding, i mean of the passage generally. as i believe was already mentioned, you're not reading to memorize every detail, but rather to know where the passage is generally going. if you do not have a fairly good idea, it's problematic to be answering any questions, although some will help you expand your basic understanding of the passage. but, you should see that that last requires you to work backwards, reverse engineer your understanding.
anyway, you tend to focus in on specific questions and certain of the accompanying answer choices. better to focus in a better understanding of the passage before rushing to get to and answer questions. of course, there is time pressure, but this is why we practice.
good luck!