A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of the text, which is about starting an indoor herb garden. It sets up the theme without going into details. It does not use any pronouns or definite articles that refer to previous ideas. Why other lines are not chosen? The other paragraphs are not chosen because they do not stand alone. For example, Paragraph 2 starts with 'Choose', which is a command and does not introduce the topic. Paragraph 3 starts with 'Once', which needs context from a previous sentence. Paragraph 4 starts with 'To maintain', which also needs earlier information.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the main ideas about starting and caring for an indoor herb garden. It gives important advice on maintenance, which is a fitting conclusion to the topic.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it continues the idea of starting an indoor garden. The phrase 'Choose a sunny windowsill' follows the action of selecting herbs, showing the next step in the process.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it follows the idea of preparing the garden. After choosing a sunny spot, the next step is to plant the herbs, which is what Paragraph 3 explains.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it talks about maintaining the herb garden after planting. It explains the need for regular watering, which is a direct follow-up to planting.