The best opening sentence names what the rest of the paragraph will discuss. A detail from sentence three is not an opening. Intro and conclusion as a set are in intro and conclusion sentences.
Topic first, example later
Read the body of the paragraph, then pick the sentence that could sit above all of it. The last-sentence version is in the best concluding sentence. Passage order is in macro logic.
The bottom line
Open with the topic. Do not open with a supporting example.
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