<p>Which underlined portion is incorrect?</p>
<p>Social scientists agree that a system for exchanging goods and services is not only present but also of necessity in all societies. </p>
<pre><code> No Error
</code></pre>
<p>I understand that of necessity is the improper part of the sentence, however, this problem took me longer than others because I could not figure out what the sentence is even trying to say. Normally I can replace an underlined portion with something that will make the sentence logical, but I cannot with this one. Hence, it took me awhile to decide between C and D. And I was correct in choosing D by instinct, but I would still like to know a more cutthroat approach to this problem. My guess is they meant "a necessity" in place of "of necessity."</p>
<p>As usual, the college board marked this problem as 'medium.' I answer all the hard problems quickly; it's the 'medium's that hold me up. I think with too much depth for this test.</p>
<p>No, they meant "necessary"; it needs to have correct parallel structure. Since "present" is an adjective, so too must the underlined phrase be. The sentence could be simplistically paraphrased as: scientists agree that such a system is present and necessary in all societies.</p>
<p>I know it's hard to do but it will help you a lot to not concentrate on what the sentence is saying, but how it is written. Try reading the parts and see if you catch anything, and then check the subject and such for dangling modifiers, etc. rather than just reading it.</p>
<p>I think that necessity is classified as a noun and, therefore, could not be preceded by "of"....has to be "a", or in another sentence, "the"....</p>
<p>No, something can be a matter "of great urgency," for example; "of course" is another very common expression in which a noun is preceded by "of." The problem with the sentence was faulty parallelism.</p>
<p>elizlan, I think you are spot on with your advice. Perhaps, had I not been focusing on the logic of the sentence I would have been able to categorize the error as faulty parallelism.</p>
<p>Thank you begoner and rodney as well. I am thinking about making a step system in which I go through the common grammar mistakes in the case that I get confused like I did here.</p>
<p>Once again though, thanks to all!</p>
<p>Is it correct to say "for exchanging?" I thought it would be "OF exchanging."</p>