A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first because it introduces the main topic of the event. It clearly states the first step in organising the event. This follows the rule of Topic Sentence. Why other lines are not chosen? The other paragraphs do not qualify as the first sentence. For example, Paragraph 2 starts with 'Once', which is a conjunction. Paragraph 3 starts with 'Equipment', which is specific and assumes prior knowledge. Paragraph 4 starts with 'Following', which also indicates a sequence and cannot stand alone.

Concluding sentence: Why this is the last line? This paragraph is the last because it wraps up the event. It shows what happens after the cleanup, which is a conclusion to the whole process.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 logically connects with Paragraph 1 because it follows a logical order. After identifying a location, the next step is to publicise the event.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 through a logical order. After publicising the event, it is important to prepare the necessary equipment.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it follows a chronological order. After the cleanup, it is logical to organise a gathering for volunteers.