A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic about seeds. It does not need another sentence to understand it. It is a general statement about the seeds. Why other lines are not chosen? The other paragraphs are not chosen because they do not stand alone. For example, "It comes from a substance called amygdalin" starts with "It" which needs more context. "This bitter taste is a defensive feature..." starts with "This" which also needs more context. "They are hard, bitter, and unpleasant" starts with "They" which refers back to something. "This chemical turns into cyanide..." starts with "This" which needs prior information.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it gives important information about the chemical. It explains the effect of amygdalin in the body. This wraps up the topic about the seeds and their danger.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it describes the seeds. The phrase "They are hard, bitter, and unpleasant" refers back to the seeds mentioned in Paragraph 1. This is the Noun Pronoun Rule.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it explains why the seeds have a bitter taste. The word "This" in Paragraph 3 refers to the bitter taste mentioned in Paragraph 2. This is the Noun Pronoun Rule.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it explains where the bitter taste comes from. The word "It" refers to the bitter taste mentioned in Paragraph 3. This is the Noun Pronoun Rule.
• Pair 4 (Paragraph 4 → Paragraph 5): Paragraph 5 connects with Paragraph 4 because it explains what happens to amygdalin. The word "This" refers to the substance mentioned in Paragraph 4. This is the Noun Pronoun Rule.