If r is an odd integer, which of the following must also be odd?  Pick one
A) 8r + 4  B) r + r  C) 3r + 3  D) 2r + r  E) r^2 + 1
Things to keep in mind:   Odd + odd = even   Odd + even = odd   Odd*odd = odd   Odd*even = even   On checking each option   A. 8r + 4   8r = even, 8r + 4 = even + even = even.   B. r + r   Odd + odd = even. This will be even   C. 3r + 3   3r = odd, 3r + 3 = odd + odd = even   D. 2r + r   2r = even, 2r + r = even + odd = odd   E. r^2 + 1   r^2 = odd, r^2 + 1 = odd + odd = even   Correct option: 2r + r
<result>D</result>
If r is an odd integer, which of the following must also be odd?