The easiest way to tell which is the answer is to quickly 
mentally substitute x=0 in 2x^2-2x+7, which easily gives +7.

Then we quickly mentally substituting x=0 in each of the choices:

a) (4x+12)+(2x^2-6x+5)

Substituting x=0 mentally in that gives 12+5 or 17, thus it
cannot be the correct choice.

b) (x^2-5x+13)+(x^2+3x-6)

Substituting x=0 mentally in that gives 13-6 or +7, thus it
is a possible choice.

c) (4x^2-6x+11)+(2x^2-4x+4)

Substituting x=0 mentally in that gives 11+4 or 15, thus it
cannot be the correct choice.

d) (5x^2-8x+120)+(-3x^2+10x-13)

Substituting x=0 mentally in that gives 120-13 or 107, thus it
cannot be the correct choice.

So the answer is (b), the only one that gave +7 when 0 was
mentally substituted for x.  This is much easier than simplifying
each one to see which simplifies to the same.  If more than one
choice had given +7 when x was substituted for x, I would then 
have also mentally substituted x=1 in those.

Edwin