Full GRE Quant Section Q:6

In this question if we take:

a=2, x=-3

b=3, y=-2

then, a+b>x+y and the answer is D.

Is there any specific reason as to why we can’t take x,y as negatives?

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Source: ETS Math Review

P.S. Highly recommend to scroll through ETS Math Review and ETS Math conventions .(Just google to find them!)