that's because require of is used as subject+verb+complement in MGMAT and here it's an adjective form required of is adjective+preposition combination (not an idiom, but close 
) I'm proud of you (proud=adjective, of=preposition)
require-verb, required-adjective
) I'm proud of you (proud=adjective, of=preposition)require-verb, required-adjective
clock60 wrote:hi guys
i wonder what is the source of the problem
i agree that the best answer is B
we need to mention firms in the first part of the sentence, and in E there is no one
such means like antecedent, and the only logical antecedent here is firms`-possessive which can`t be valid antecedent for such
but in B i see also idiom problem
MG sentence correction page 165
according to them
require of x to do y is wrong
example
she requires of her friend to do work this usage is not valid
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