A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of wheat. It does not use any pronouns or definite articles that need prior context. It gives a broad overview of wheat as a crop. Why other lines are not chosen? Paragraph 2 starts with 'It', which is a pronoun and needs context. Paragraph 3 starts with 'Moreover', which is a conjunction and shows continuation. Paragraph 4 starts with 'Conversely', which also shows a contrast and is not independent.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion about wheat. It highlights the challenges of wheat cultivation, which gives a complete view of the topic. It does not introduce new ideas but summarizes the issues related to wheat.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): The second paragraph connects to the first because it gives more information about wheat. This follows the Broader to Specific Strategy, where the first paragraph gives a general idea about wheat, and the second paragraph provides specific details about its importance as food.
• Pair 2 (Paragraph 2 → Paragraph 3): The third paragraph connects to the second because it adds more details about wheat. The word 'Moreover' is a connector that shows this addition of information. This follows the Connector Strategy.
• Pair 3 (Paragraph 3 → Paragraph 4): The fourth paragraph connects to the third because it shows a different side of wheat. The word 'Conversely' indicates a contrast, which is part of the Contrast Strategy. It shows that while wheat is useful, there are also challenges in its cultivation.