Which of the following polynomials is a perfect square trinomial?
x2+6x+36x^2 + 6x + 36x2+6x+36
4x2−12x+94x^2 - 12x + 94x2−12x+9
x2+10x−25x^2 + 10x - 25x2+10x−25
9x2+6x+49x^2 + 6x + 49x2+6x+4