If S is a positive integer, which of the following must be odd?	Choose the correct choice from the following answers.
A) S+1
B) S^2+S
C) S^2+S+1
D) x^2−1
E) 3x^2−3
A. S+1 = can be odd or even. Since O + O =E or E + O = O   B. S^2 + S = S(S+1). Since from the above derivation we already know the term S+1 can be Odd or Even, directly substitute here. S(ODD) = Even (When S is Even) or S(EVEN) = EVEN [When S is ODD]   C. Here's the answer. Since we know the term S^2 + S can always take a EVEN number, EVEN + 1 = ODD   Hence S^2+S+1.
<result>C</result>
If S is a positive integer, which of the following must be odd?