Which polynomial is prime?

x4 3x2 - x2 - 3

x4 - 3x2 - x2 3

3x2 x - 6x - 2

3x2 x - 6x 3

X^4 + 3x^2 - x^2 - 3 = x^2 (x^2 + 3) - 1 (x^2 + 3) = (x^2 - 1) (x^2 + 3)

x^4 - 3x^2 - x^2 + 3 = x^2 (x^2 - 3) - 1 (x^2 - 3) = (x^2 - 3) (x^2 - 1)

3x^2 + x - 6x - 2 = x (3x + 1) - 2 (3x + 1) = (x - 2) (3x + 1)

3x^2 + x - 6x + 3 = x (3x + 1) - 3 (2x - 1); since the content of the two bracket are not the same for this polynomial, that mean it is not factorisable and hence a prime.

The answer is D on edge unity