Correct answer: None of these
Option (a) sin[log(x+sqrt(x^2+1))] uses the odd function sinh^-1(x), so it is odd. Option (b) has an even numerator over an odd denominator (x^3 + x^4 cot x is odd), giving an odd function. Option (c) is Cauchy's equation forcing f(0)=0 and f(-x)=-f(x), odd. None is even, so answer is None of these.