<p>Future plans for the park will be announced this Sunday during a special ceremony to <strong>mark</strong> its 15th anniversary.</p>
<p>The correct answer is <strong>(D) mark</strong>.</p>
<p>The verb "mark" is used in this context to mean "to celebrate" or "to commemorate" an important event, in this case, the 15th anniversary of the park. The phrase "to mark an anniversary" is a common expression that indicates the act of recognizing or acknowledging a specific milestone or date.</p>
<p>The other options do not fit the context as well:</p>
<p>(A) "raise" does not make sense in this context because it does not convey the idea of celebrating or recognizing an anniversary.</p>
<p>(B) "hold" could work grammatically, but it does not capture the intended meaning of celebrating the park's anniversary.</p>
<p>(C) "regard" does not fit the context because it means "to consider" or "to view" something in a certain way, which is not the intended meaning here.</p>