A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first line because it introduces the main topic of translation technology. It does not use any pronouns or definite articles that refer to previous ideas. It also gives a broad overview of the subject without going into specifics. Why other lines are not chosen? Paragraph 2 starts with 'Machine', which is a pronoun that refers back to the previous sentence. Paragraph 3 starts with 'However', which is a conjunction. Paragraph 4 starts with 'As a result', which is also a conjunction. Therefore, they do not qualify as independent sentences.

Concluding sentence: Why this is the last line? This paragraph is the last line because it summarizes the main idea of the text. It shows the importance of human translators after discussing the limitations of machine translation tools.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 logically connects with Paragraph 1 because it continues the topic of translation technology. The phrase 'Machine translation tools' builds on the idea of advances in technology.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it discusses the improvements of machine translation tools. The word 'However' shows a contrast, indicating that despite improvements, there are still issues.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it explains the consequence of the struggles mentioned. The phrase 'As a result' shows that human translators are needed because of the limitations of machine tools.