May a paragraph contain only one sentence?

Yes. In fact, a paragraph with a single sentence is very emphatic because it stands out compared to other longer paragraphs which may surround it.

Varying the length of paragraphs helps stimulate reader interest. Obviously, the length of a paragraph depends on its content. However, a great deal of latitude is possible: A single-sentence paragraph can be used to simply state a position or point. Then, explanatory paragraphs which follow can be longer, providing necessary examples and details.