<p>So on Princeton Review-Cracking the SAT, there is a writing question that's a bit confusing:</p>
<p>Forest fires, long (thought to be) a detriment to the environment, (are) now understood (not only) to be unavoidable but also to be (a boon) to the forests.</p>
<p>The answer key says No error, but wouldn't the answer be (a boon), with the correct answer being "boons"?</p>
<p>sorta, yeah, but it’s already been established that the sentence considers “forest fires” to be a single phenomenon (“a detriment,” a phrase you can’t change). Not a great Q.</p>
<p>Based on your question stripping down the sentence to its essence, we have:</p>
<p>Fires are a boon to the forests.</p>
<p>Subject: fires
Verb: are
Object: boon</p>
<p>In English you must have subject-verb agreement. But there is no requirement for subject-object agreement. So the subject can be plural and the object singular.</p>
<p>Consider:</p>
<p>Most students prefer music to art.</p>
<p>They took the elevator to the top floor.</p>
<p>Etc.</p>
<p>The key to the sentence is that it is referring to fires as a group and their combined impact on the environment when it says they are a boon and thus boon is singular.</p>
<p>The notion that there’s no need for subject-object agreement is reductive. Noun-number agreement does come up on the exam (most common pattern: “Bob and Mary both want to be a veterinarian when they grow up.”).</p>