First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic. It tells us what sherbet powder is. This is a general statement that does not need other sentences for context. It does not start with a conjunction or use pronouns. Why other lines are not chosen? Paragraph 2 starts with "In this way," which is a transitional phrase. Paragraph 3 starts with "This process," which uses a pronoun that refers back to something else. Paragraph 4 starts with "When it is mixed," which also uses a pronoun. All these reasons make them not independent.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the topic. It shows how the information about sherbet powder and endothermic reactions relates to cold packs. It gives a clear conclusion to the discussion.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it explains what happens when sherbet powder is mixed with water. This shows a logical order from the introduction of sherbet powder to its reaction.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it explains the endothermic process. It gives more details about the reaction mentioned in Paragraph 2. This is a broader to specific strategy.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it shows how the endothermic process works in a cold pack. It gives an example of the process discussed in Paragraph 3. This is a topic example strategy.