If s is an odd integer, which of the following must also be odd?
Choose the correct choice from the following choices:
A) 2s + 6 B) s + s C) 3s + 3 D) 2s + s E) s^2 + 1
Things to keep in mind:   Odd + odd = even   Odd + even = odd   Odd*odd = odd   Odd*even = even   On checking each option   A. 2s + 6   2s = even, 2s + 6 = even + even = even.   B. s + s   Odd + odd = even. This will be even   C. 3s + 3   3s = odd, 3s + 3 = odd + odd = even   D. 2s + s   2s = even, 2s + s = even + odd = odd   E. s^2 + 1   s^2 = odd, s^2 + 1 = odd + odd = even   Correct option: 2s + s
<result>D</result>
If s is an odd integer, which of the following must also be odd?