A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of competition in early human history. It does not refer to any previous information and sets the stage for the following ideas. It is a general statement about early man. Why other lines are not chosen? Paragraph 2 starts with 'But', which is a conjunction. Paragraph 3 starts with 'Indeed', which is also a conjunction. Paragraph 4 starts with 'I am sure', which is a personal statement and not general. Paragraph 5 starts with 'The last creature', which uses 'the' and assumes prior knowledge.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion about competition with creatures. It provides a final example and shows how humans have overcome this competition, bringing closure to the topic.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it uses the connector 'But' to show a change from the past to the present. It indicates that the competition mentioned in Paragraph 1 is no longer relevant.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 follows Paragraph 2 logically because it explains why the phase is finished. It shows that we do not have the skills needed for primitive conditions, linking the ideas clearly.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it gives a personal example of lacking experience. It shows how this lack affects our ability to deal with dangerous animals.
• Pair 4 (Paragraph 4 → Paragraph 5): Paragraph 5 connects to Paragraph 4 because it continues the theme of competition with creatures. It introduces the mosquito as another example of a creature that once competed with man.