A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of the text. It talks about proteins and their role in plant growth. This is a general statement that sets the stage for the following sentences. It does not use any words that need prior context. Why other lines are not chosen? Paragraph 2 starts with 'Understanding this process' which needs context from the first sentence. Paragraph 3 starts with 'They can help' which refers back to proteins, so it cannot stand alone. Paragraph 4 starts with 'In the future' which also needs earlier information to make sense.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the ideas presented in the text. It talks about applying the knowledge to crops in the future, which concludes the discussion about proteins, plant growth, and drought.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it continues the idea of how proteins help plants. The phrase 'They can help' refers back to the proteins mentioned in Paragraph 1. This shows a logical flow of ideas.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 follows Paragraph 2 because it explains why helping plant roots is important. The phrase 'Understanding this process' shows that knowing how proteins help roots leads to finding out about grains that can survive drought.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it talks about the future use of the knowledge gained from understanding how grains survive drought. The phrase 'In the future' shows the next step after understanding the process.