After simplification of Quantity A
$(x-2)^2$ = $x^2$ + 4 - 4x

We can subtract $x^2$ from both Quantity A and Quantity B, because it will not have any impact i.e the greater quantity will remain greater and by same margin.

So we'll get:

Quantity A: 4 - 4x
Quantity B: 4x

Similarly, we can add 4x on both Quantities, because it will not impact or change the greater quantity to less quantity.

Thus, we'll get

Quantity A: 4
Quantity B: 8x

As we don't know whether x is positive, 0 or negative. So Choice D is correct.