A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of setting up a home aquarium. It gives a broad overview of what to do first without going into details. It does not use any pronouns or definite articles that refer to previous information. Why other lines are not chosen? Paragraph 2 starts with "After securing the tank," which refers to something that is not mentioned before. Paragraph 3 starts with "Installing the filtration system," which also assumes prior knowledge. Paragraph 4 starts with "The introduction of live plants," which uses the definite article "the" and assumes prior context. Paragraph 5 starts with "Finally," which suggests it is not the first sentence.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the process of setting up the aquarium. It uses the word "finally," which signals that this is the conclusion of the steps.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): There is a logical order here. After choosing the tank size, the next step is to secure the tank. This shows a clear flow of ideas.
• Pair 2 (Paragraph 2 → Paragraph 3): The second paragraph talks about adding substrate, and then the third paragraph explains the importance of the filtration system. This shows a logical order of steps in setting up the aquarium.
• Pair 3 (Paragraph 3 → Paragraph 4): The third paragraph discusses the filtration system, and then the fourth paragraph introduces live plants. This shows a broader to specific strategy, as plants are an important part of the aquarium.
• Pair 4 (Paragraph 4 → Paragraph 5): The fourth paragraph talks about live plants, and the fifth paragraph concludes with introducing the fish. This shows a logical order, as you add plants before introducing the fish.