A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic, Helen Keller. It gives a clear starting point for the story. It does not use any pronouns or definite articles that need prior context. Why other lines are not chosen? Paragraph 2 starts with 'When she was six,' which needs prior context. Paragraph 3 starts with 'She became mute,' which also needs prior context. Paragraph 4 starts with 'She became very ill,' which again needs prior context. All these sentences cannot stand alone without referring back to Helen Keller.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the story of Helen Keller's education and success. It shows the result of all the events that came before it.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): This pair connects because the second sentence gives more details about Helen Keller's early life after her birth. It follows a logical order of events.
• Pair 2 (Paragraph 2 → Paragraph 3): This pair connects because the third sentence explains what happened after she became blind and deaf. It shows a clear cause and effect relationship.
• Pair 3 (Paragraph 3 → Paragraph 4): This pair connects because the fourth sentence shows the next important step in her life after becoming mute. It follows a logical order of events.
• Pair 4 (Paragraph 4 → Paragraph 5): This pair connects because the fifth sentence explains the success of Helen's education after she started learning from Anne Sullivan. It shows a logical progression from learning to achievement.