A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of the text. It uses the rule of Topic Sentence. It tells us that chronobiologists study the circadian rhythm in humans. Why other lines are not chosen? Other paragraphs are not chosen because they do not stand alone as the first sentence. For example, Paragraph 2 starts with "This is" which needs prior context. Paragraph 3 starts with "Aside from" which also needs context. Paragraph 4 starts with "Not everyone" which refers back to a previous idea. Paragraph 5 starts with "'Night people'" which is an example and needs a topic before it.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it provides an example that wraps up the discussion about circadian rhythms. It uses the rule of Summary Style. It shows how individual differences affect people, which connects back to the main topic.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it gives a complete overview of the circadian rhythm. This follows the Broader to Specific Strategy. The first sentence introduces the topic, and the second sentence explains what the circadian rhythm is.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it gives more details about the cycle mentioned in the second paragraph. This follows the General to Specific Strategy. The second paragraph talks about the cycle, and the third paragraph explains other factors involved in that cycle.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it introduces a new idea about individual differences in circadian rhythms. This follows the Logical Order strategy. The third paragraph talks about the cycle, and the fourth paragraph shows that not everyone experiences it the same way.
• Pair 4 (Paragraph 4 → Paragraph 5): Paragraph 5 connects with Paragraph 4 because it gives an example of the differences in circadian rhythms. This follows the Topic Example strategy. The fourth paragraph states that not everyone has the same rhythm, and the fifth paragraph gives an example of 'night people'.