Final answer:
Above-the-line deductions reduce a taxpayer's AGI, potentially increasing the deductibility of below-the-line deductions that have AGI limitations.
Step-by-step explanation:
The sentence should be completed as follows: Deductions above AGI cause a reduction in AGI, which increases the deductibility of differences below AGI deductions subject to AGI limitations. Above-the-line deductions, those that occur above the AGI line on a taxpayer's income statement, reduce a taxpayer's adjusted gross income (AGI). This, in turn, has the potential to increase the deductibility of below-the-line deductions - those which are taken from AGI - as these often have limitations based on the taxpayer's AGI. For example, certain itemized deductions are only deductible to the extent that they exceed a certain percentage of the taxpayer's AGI.