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 experiment. It states the hypothesis clearly, which is the main idea of the text. This follows the rule of Topic Sentence. Why other lines are not chosen? The other paragraphs are not chosen because they do not stand alone as the first sentence. For example, 'To test this...' starts with a conjunction, so it cannot be first. 'Another group of plants...' uses 'another,' which refers back to the first group, so it cannot be first. 'Over several weeks...' talks about results, which need a setup first. 'This outcome...' also refers to previous information, so it cannot be first.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the main idea of the text. It summarizes the results and shows the conclusion of the experiment. This follows the rule of Conclusive Words.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it shows the next step in the experiment. The phrase 'To test this' is a clear connector that shows the logical order of the experiment.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it explains what was done next in the experiment. It shows the logical order of having a control group to compare with the first group.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it presents the results of the experiment. It shows the logical order of what happened after the control group was established.
• Pair 4 (Paragraph 4 → Paragraph 5): Paragraph 5 connects with Paragraph 4 because it explains the meaning of the results. The phrase 'This outcome' refers back to the results mentioned in Paragraph 4, showing a cause and effect relationship.