When calculating the annual tax deducted at the end of the year, it is sometimes difficult to predict whether an income will surpass a certain bracket.

(A) When calculating the annual tax deducted at the end of the year, it is sometimes difficult to predict whether an income will surpass a certain bracket

(B) When calculating the tax deducted at the end of the year, it is sometimes difficult to predict if an income will surpass a certain bracket

(C) It is sometimes difficult to predict whether or not an income will surpass a certain bracket when calculating the tax deducted annually

(D) When calculating the tax deducted at the year's end, it is sometimes difficult to predict whether an income will surpass a certain bracket

(E) When calculating the tax deducted at the end of the year, it is sometimes difficult to predict whether an income will surpass a certain bracket or not

Correct answer is D.

My questions are:
1. Is the use of '' year's '' in answer D correct? As far as i know, 's is only allowed with concrete/tangible nouns to express possession. Would appreciate any expert's opinion to clear my concept in this regard.
2. Is the use of 'or not' with 'whether' is wrong?