Which polynomial is prime?

x3 + 3x2 – 2x – 6
x3 – 2x2 + 3x – 6
4x4 + 4x3 – 2x – 2
2x4 + x3 – x + 2

The polynomial that is prime is 4x^4 + 4x^3 - 2x - 2.