<p>One reason is the drivers.
One reason are the drivers.</p>
<p>The McGraw-Hill book says it’s the latter, but I simply don’t get it.</p>
<li>Since/Because
Is it “WRONG” to use since?
I know because is “preferred,” but in sentence error section, should I change since to because?</li>
</ol>
<p>I'd say "one reason is the drivers" as the subject of the sentence is singular therefore "is". I don't think you can change the order of the sentence around like spirited away is suggesting, as that allows for 2 different interpretations of the sentence, both of which are correct</p>
<p>"One reason is the drivers" is not a sentence. If "one reason" were a subject, and "is" the verb, then "the drivers" wouldn't be a valid object for the verb. It doesn't mean anything. You could, however, say that "One reason is that the drivers etc..."</p>
<p>With "One reason are the drivers," the word order might throw someone off, but it actually is saying something. By changing it to "The drivers are one reason," you are only changing the word order or the presentation, not the meaning of the sentence or the function of the individual words. It's the equivalent of saying "Good are the kids" or "Interesting is the book that evokes." To change either to "The kids are good" or "The book that evokes is interesting" changes nothing in the way of meaning or function.</p>
<p>Therefore, "One reason are the drivers," is a valid sentence, while the former isn't.</p>