GMAT prep

wow, that's annoying; the side ads are coming right down in the middle of the image file. (this may be the reason that this post has 0 responses so far.)

i had to right-click (control-click, on a mac) and select "open image in another tab/window".

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you're looking for a NECESSARY ASSUMPTION. the question prompt is certainly ugly, but that's what it means. (if you see "could not result unless...", then you know you're looking for a NECESSARY ASSUMPTION.)

remember that NECESSARY ASSUMPTIONS MUST BE RELEVANT TO THE CONTENT OF THE PASSAGE. they can't be random new facts.

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the passage makes no mention of the effects of lowering tax rates, so your choice is out of scope.
the passage mentions only what happens at current tax rates when tax evasion occurs: the rates are hiked.

also, importantly, "NO ONE" is an EXTREMELY suspicious phrase. remember that you're looking for a NECESSARY ASSUMPTION here - i.e., something that's REQUIRED if the passage is to have any validity. this "no one" is clearly not a REQUIRED assumption: even if there are a few people who would take such action if tax rates were lowered, the passage's logic would still be fine.

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the reason why (c) is correct lies in the following sentence: "tax evasion forces lawmakers to raise income tax rates."
if that's true, then this MUST mean that tax evasion causes a SHORTFALL OF TAX REVENUE; there is no other possible reason that lawmakers could be "forced" to raise income-tax rates.