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

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion. It shows a conclusion about the negative impact of soy cultivation, which reflects the overarching theme of the text.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it continues the topic of soybeans. It gives a specific example of how soybeans are used, showing a logical order from general to specific.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it adds more information about soybeans. It shows another important use of soybeans, which is a logical order of ideas.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it introduces a contrast. It shows a negative effect of soy cultivation, which is linked to the previous positive uses of soybeans.