First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of endothermic reactions. It clearly states what an endothermic reaction is without needing any other context. This follows the rule of Topic Sentence. Why other lines are not chosen? Paragraph 2 starts with 'For example,' which is a conjunction and needs prior context. Paragraph 3 starts with 'When it is mixed,' which also needs context. Paragraph 4 starts with 'Another example,' which refers back to previous information. Paragraph 5 starts with 'This process,' which uses a pronoun that refers to something not yet introduced.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion about endothermic reactions. It summarizes how cold packs work and relates back to the main topic. This follows the Summary Style rule.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it uses the word 'For example,' which shows it gives an example of the endothermic reaction mentioned in Paragraph 1. This follows the Connector Strategy.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it explains what happens when sherbet is mixed with water. This follows the Broader to Specific Strategy, as it gives more detail about the example.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it gives another example of an endothermic reaction. This follows the Logical Order rule, as it continues the topic of endothermic reactions.
• Pair 4 (Paragraph 4 → Paragraph 5): Paragraph 5 connects with Paragraph 4 because it explains how the cold packs work, which is related to the endothermic reaction discussed in Paragraph 4. This follows the Topic Example rule.