A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main idea about worry. It is a general statement that does not need other sentences for context. It does not use any pronouns or definite articles that refer to previous ideas. Why other lines are not choosen? The other paragraphs are not chosen because they do not stand alone. For example, Paragraph 2 starts with 'It is useless,' which needs context. Paragraph 3 starts with 'And if,' which is a conjunction. Paragraph 4 uses 'this something else,' which refers back to an idea not yet introduced.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the ideas. It shows how to overcome worry and ends the discussion on the topic. It provides a conclusion to the earlier points.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it continues the idea of worry. The phrase 'in this condition' refers back to the state of the mind mentioned in Paragraph 1. This shows a logical order of ideas.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it explains why arguing is useless. It shows that having a strong will does not help, which is a cause and effect relationship.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it gives a solution to the problem. It explains what can help when the will is not enough. This shows a broader to specific strategy.