How should Mr. Muldoon respond to the student who refuses to participate in the metric conversion activity?

Mr. Muldoon's best approach is to explain the many ways in which people in America use the metric system. This response can help the student understand the relevance and importance of the metric system in real-life situations, such as in science, medicine, and international contexts. By providing context and examples, Mr. Muldoon encourages the student to see the value in the activity and may foster a willingness to participate.

Engagement through education is often more effective than punitive measures. In contrast, simply excusing the student or administering a detention does not address the underlying issue of the student's reluctance to participate. Additionally, giving a zero for participation without attempting to engage the student could further alienate them and discourage future participation. Thus, using explanation to highlight the practicality and utility of the metric system is the most constructive response.