On an increasing difficulty scale from 1 to 10 I think this passage fits 7 as it is big and asks many questions on supporting ideas which requires one to look into the passage again.
On your second question, I will suggest you to skim through the passage noting the "dynamics of the flow of ideas". Keep those "turns" in your mind, no need to write and waste time. Improve your short term memory to facilitate this. Also note the main idea of the passage, the most important point in the passage. The questions related to main idea or the passage as a whole can be answered easily. For questions requiring specific parts of the passage, go back to that particular part of the passage re-read and answer the question.
I hope this will work, practice more...even I am struggling to synchronize my mind with the passages whose topic I don't like.
Practice is the only way out...
The answers to the passage are:-
61.(D) as the passage introduces a method of understanding the native american culture and then goes on to write its disadvantages.
62.(C) The author writes that the ethnologists do not know the language of the natives
63.(A) given in the first para
64.(E) the author tells that the information is distorted or edited.
65.(C) main idea
66.(B) clearly written in the passage
I hope this helps...
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