If x is a positive integer, which of the following must be odd?
Choose the correct choice from the following answers:
A) x+1 B) x^2+x C) x^2+x+9 D) x^2−1 E) 3x^2−3
A. X+1 = can be odd or even. Since O + O =E or E + O = O   B. X^2 + X = X(X+1). Since from the above derivation we already know the term X+1 can be Odd or Even, directly substitute here. X(ODD) = Even (When X is Even) or X(EVEN) = EVEN [When X is ODD]   C. Here's the answer. Since we know the term x^2 + X can always take a EVEN number, EVEN + 9 = ODD   Hence x^2+x+9.
<result>C</result>
If x is a positive integer, which of the following must be odd?