Every even integer can be written as 2n where n is any integer even or odd.

Every odd integer is one more than an even integer, so every odd integer can be
written as an even integer, 2n, plus 1 or 2n+1, where n is any even integer,
even or odd.  (Note: 0 is considered an even integer)

So the product of an even integer and an odd integer is

2n times 2n+1 or

2n(2n+1)

or multiplying that out

4n²+2n

That's why the answer is D)

Edwin