D is a prime polynomial.
The best way to figure this out is by attempting to factor them all. Each of them factors into perfect squares except for D.
A)
x^2 - 6x + 9 = (x - 3)^2
B)
x^2 + 16x + 64 = (x + 8)^2
C)
4x^2 + 20x + 25 = (2x + 5)^2
D we can also tell won't have a perfect square like that because it ends in a negative number. No number multiplied by itself is negative.