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, which is the cold summer in 1816. It does not refer to any previous information and sets the stage for the following details. This follows the rule of Topic Sentence. Why other lines are not chosen? The other paragraphs are not chosen because they do not stand alone. For example, Paragraph 2 starts with "Particularly" which is a connector. Paragraph 3 starts with "At the time" which also needs context. Paragraph 4 starts with "Nowadays" which refers to the present and needs earlier context.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion by providing a conclusion about the speculation. It uses the phrase "Nowadays, scientists believe" which signals a final thought. This follows the Conclusive Words rule.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it gives more details about the cold summer. This follows the Broader to Specific Strategy. The first sentence talks about the cold summer, and the second sentence explains what happened in New England.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it talks about the reactions to the cold summer. This follows the Logical Order rule. The second sentence describes the effects of the cold summer, and the third sentence explains the speculation about the weather.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it gives a possible reason for the speculation. This follows the Cause and Effect Relationship rule. The third sentence talks about speculation, and the fourth sentence provides a scientific explanation.