The philosophy of the Founding Fathers, the political and military leaders who led the country to its independence,
have been the subject of an increasing amount of biographies.
Meaning analysis: the philosophy of some leaders has been the reason for subject of many biographies
Error analysis: question tests subject-verb agreement error, and idiom.
Subject “The philosophy” doesn't agree in number with plural “have”.
Usage of “amount” is incorrect, since we use “amount” only with uncountable nouns (amount of music). But here “biographies” is plural, hence it has to take idiom “number”
a)
have been the subject of an increasing
amountb)
have been the subject of an increasing number
c)
have subjected an increasing number
(distorts the meaning of the original sentence, it implies that the philosophy itself exposing the number of biographies)d) has been the subject of an increasing
amounte) has been the subject of an increasing numberSo to me
E is correct
(please correct if you see any mistakes or gaps in my explanation, thank you)