You want to spend most of your time and energy on the easier questions; which is the first half of the LR section, as they will require less effort to get them correct, for they are not as difficult as the second half.

NA, as if the negated version of the answer choice hurts the argument, then it is the correct answer, it works 100% of the time on all different degrees of NA difficulty.

initially, i thought C was correct, but my failure to correctly read the stem had me choosing answer choice E

not mixing the sufficient and necessary conditions for an answer choice is key, which would help you pick B over E.