fameatop
A 1999 tax bill changed what many wealthy taxpayers and large corporations are allowed to deduct on their tax returns.
it's a general fact. a bill changed smth what people now are allowed. so A works fine.
A) changed what many wealthy taxpayers and large corporations are allowed to deduct on their tax returns.
looks good, SV are in proper tenses/forms, pronouns have clear antecedents.
B) changed wealthy taxpayers' and large corporations' amounts that they have been allowed to deduct on their tax returns.
the bill changed what people are allowed to deduct on tax returns, not the amounts. moreover, present perfect tense is not correct. pronoun their has no clear antecedent.
C) is changing wealthy taxpayers' and large corporations' amounts that they have been allowed to deduct on their tax returns.
bill is already in force, so no need for present progressive. they/their have no clear antecedent. same mistake as in B - is changing amounts...
D) changed what many wealthy taxpayers and large corporations had been allowed to deduct on their tax returns.
tricky one, was thinking between A and D, but since the bill is still in effect, A is better.
E) changes what many wealthy taxpayers and large corporations have been allowed to deduct on their tax returns.
changes - incorrect. have been allowed - not needed