<li>(Introducing) new ideas and replacing (old ones) (is) always a highly controversial matter, especially (when) there is already tension between an older a a younger generation.</li>
</ol>
<p>Obviouslym “is” is wrong. Since two things are connected by the conjunction AND, the verb followed should be plural.</p>
<p>Anyhow, the blue book says the answer is NO error. Anyone can explain this?</p>
<p>First of all, College Board is correct. In the sentence, "(Introducing) new ideas and replacing (old ones)" functions as a single unit and is therefore a singular subject requiring the correct verb "is." Just because they're joined by and doesn't mean that it's plural.</p>
<p>For example:</p>
<p>"Milk and cereal IS my favorite breakfast."</p>
<p>
[quote]
"a highly controversial matter" is singular</p>
<p>that means the verb has to be singular
[/quote]
</p>
<p>This is not true. In literature, especially in metaphors, singular subject/plural predicate nominative is often used. Quick example:</p>