understanding CR stimulus

[pcmdotcom]

I have been following the Power Critical Reasoning Bible book for my prep. I have realized that I am very good at figuring out the premise, conclusion and other important information in a short passage. My problem is that even though I can figure these things out, sometimes I just don't understand the information given in the passage. Most of the time it has to do with subjects relating to art and archeology. Can anyone please guide me as to what I should do to better understand the passages? Is it due to lack of concentration or should I keep practicing until I eventually get how to solve the problems?

[TheGmatTutor]

As you read the evidence, you could try jotting down brief notes that follow the logic of the passage. For example, for question 105 in the Official Guide (pg. 532), you might write down:

Cost of radios in Q: 10% less than Y
Cost of radios in Q + tariffs: still less than Y

(A)Not necessarily true
(B)Outside the scope
(C)Correct - tariff must be less than 10% of the cost
(D)Contradicts
(E)Outside the scope