A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic. It tells us about the first tank called Little Willie. It does not need any other sentence to understand it. It does not use any words that need prior context. Why other lines are not chosen? Paragraph 2 starts with 'It' which is a pronoun, so it needs the first sentence for context. Paragraph 3 starts with 'Then' which is a conjunction, so it cannot be first. Paragraph 4 starts with 'They' which is also a pronoun, so it needs prior information.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the topic. It shows the final result of the improvements made to the tanks. It gives a clear conclusion about how tanks can now cross battlefields.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it gives more details about the tank. This follows the Broader to Specific Strategy. The first sentence talks about the tank, and the second sentence explains its weight and problems.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it talks about improvements after discussing the problems of the tank. This follows the Logical Order rule. The second sentence describes issues, and the third sentence shows that changes were made.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it explains the result of the improvements. This follows the Cause and Effect Relationship rule. The third sentence talks about improvements, and the fourth sentence shows how these improvements help current tanks.