The correct answer is: A. Zero
When decoding a cyclic code, the received code word is compared to the transmitted code word. If the received code word is similar as transmitted code word, then the remainder of the division of the received code word by the generator polynomial, $g(x)$, is zero. This is because the generator polynomial is a polynomial that represents all possible code words, and if the received code word is a code word, then it must be a multiple of the generator polynomial.
Option B is incorrect because unity is not a possible remainder when dividing a code word by the generator polynomial. Option C is incorrect because infinity is not a valid number in mathematics. Option D is incorrect because it is not one of the possible answers.