A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first because it introduces the main topic. It talks about Australia's native plants and animals and their long history. This is a broad overview of the subject. It does not use any words that need prior context. Why other lines are not chosen? Paragraph 2 starts with 'Since European settlement' which needs prior context. Paragraph 3 starts with 'Some' which is a pronoun and needs more information. Paragraph 4 starts with 'These' which also refers back to something not yet mentioned.

Concluding sentence: Why this is the last line? This paragraph is the last because it sums up the main points. It shows the overall impact of the challenges on the environment. It brings together the ideas from the previous paragraphs.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): The second paragraph connects to the first because it shows a change. The first talks about how plants and animals lived for a long time. The second shows how things changed after European settlement. This is a logical order.
• Pair 2 (Paragraph 2 → Paragraph 3): The third paragraph connects to the second because it continues the idea of challenges. The second talks about competition with introduced animals. The third adds that some native species face new predators. This shows a logical order of challenges.
• Pair 3 (Paragraph 3 → Paragraph 4): The fourth paragraph connects to the third because it explains the result of the challenges. The third talks about facing predators, and the fourth shows how these pressures affect the environment. This is a cause and effect relationship.