If you observe G(x) and F(x), you can find F(x) is obtained by just moving G(x) 4 units upwards.
This means F(x) is obtained after vertical translation of G(x). This vertical translation can be expressed by adding 4 to G(x).
So,
F(x) = G(x) + 4
F(x) = x² + 4
So, the correct answer is option D