The word "penultimate" means "next to the last" or "second to the last" in a series of things.

It can also be used to describe the next to the last syllable of a word. In this context, the word "penultimate" is used to describe the paragraph of the essay that comes before the last one.

It implies that the essay has only two more paragraphs to be written.

Therefore, the option that is nearest in meaning to "penultimate" is A. last but one. This means the one that is immediately before the final one.