Math Destroyer Question

[Ibraiz]

http://img64.imageshack.us/img64/696/mathdestroyer.jpg

Why is Answer choice A not correct? The explanation in Math Destroyer for correct answer choices, wouldn't it be the same explanation for answer choice A?

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[sfoksn]

Because P+Q isn't always positive, you see, what if you had -2 as Q and -3 as P?

 

[Ibraiz]

Because P+Q isn't always positive, you see, what if you had -2 as Q and -3 as P?

Thanks Sfoksn, it makes sense when I plug in those numbers in the equation.