<p>The cost of (safely disposing) of the toxic chemicals (is approximately) (five times what) the company paid (to purchase it). (No error)</p>
<p>So I said "A" because the use of the word "of" twice seemed awkward and didn't flow well, but the correct answer was "D" - I now know that this is because it should have been "purchase them"...however, I am confused as to why there is nothing wrong with choice "A"...any thoughts?</p>
<p>How else would you say the part that includes A? And regardless, I.D.E. doesn’t test good writing like I.S., only formal rules being broken (like in choice D). Unless a rule is being broken there is no error.</p>
<p>“cost of” and “disposing of” are both proper verb/preposition phrases. Since grammar does not limit the following a verb phrase with another phrase that modifies it, so long as the propositions are correct, the sentence is correct. </p>
<p>I think that “the cost of safe disposal of the chemicals” makes more sense, but obviously there is a plurality problem with D, so that one is more incorrect.</p>