TL; DR The answer is A.

Quadratic functions have a degree of two.

This means the range will always either tend towards - ∞ or + ∞, but not both.

Think about some cases:

a>0

2x^{2}+x+1. at extreme positive or negative values (x=10000000/-1000000000) this function tends towards +∞ and not to -∞

a<0

-2x^{2}-x+1. at extreme positive or negative values (x=1000000/-10000000) this function tends towards -∞ and not to +∞.

Hope this helps, let me know if you have further questions.