Hi Moal,
We can offer lots of clarification. Let me refer you to a great thread where this question has been discussed before:
lsat/viewtopic.php?t=7333&p=18851&hilit ... int#p18851
And for me, I always found it easier to do MP questions last, after working through the rest of the questions for that passage. You will likely have a much better grasp of the main point after working with the passage for 8-9 minutes. Alternatively, answer the MP first but double-check your answer before moving to another passage.
Also, when all the answers seem equally bad, go for the answer that 1) you can prove: these are still Prove-family questions, and 2) that covers the most textual "real estate" so to speak. Correct MP answers rarely focus on a single paragraph of the passage.
Thanks for the great question and I hope this helps!
