One or more sentences about a single idea is best termed
a. a. topic,
b. main idea,
c. paragraph,
d. conclusion

The correct answer is letter C. Paragraph. One or more sentences about a single idea is best termed as paragraph. A paragraph is compose of many sentences where there is a main idea and supporting ones. The reason for that is because we need to have coherence in a paragraph in order for it to make sense.

One or more sentences about a single idea is best termed a paragraph. When we're using paragraphs, we're usually writing about the same topic and the same idea in a longer way, to present our case more cleary and be more concrete about what we're talking about.