In a test paper, a question is given as :
Let, x1^x2^x3^x4 =0 where x1, x2, x3, x4 are Boolean variables,and ^ is the XOR operator. Which one of the following must always be TRUE? (A) x1x2x3x4 = 0 (B) x1x3+x2 = 0 (C) x1'^x3' = x2'^x4' (D) x1+x2+x3+x4 = 0 + is OR and concatenation is AND operator.
Correct answer is C, which I guessed because when all booloean variables are 1, then, neither A,B, or D will hold,But what is the correct way to get to option C?