A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first line because it introduces the main topic of turfgrass. It explains what turfgrass is and how it works. This is an introductory statement that sets the stage for the following information. It does not refer to any previous context, making it independent. Why other lines are not chosen? Paragraph 2 starts with "An average sized healthy lawn..." which is specific and does not stand alone. Paragraph 3 starts with "Because of this..." which refers back to previous information. Paragraph 4 starts with "In addition to..." which also refers to earlier ideas. All these sentences do not meet the criteria for being independent.

Concluding sentence: Why this is the last line? This paragraph is the last line because it summarizes the benefits of turfgrass. It adds more information about how turfgrass helps the environment. This wraps up the discussion about turfgrass and its positive effects.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 logically connects with Paragraph 1 because it continues the topic of turfgrass. The first paragraph explains what turfgrass does, and the second paragraph gives specific examples of how much carbon it can capture. This shows a logical order from general information to specific details.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it explains the importance of the information given in the second paragraph. The phrase "Because of this" shows a cause and effect relationship. The capture of carbon leads to the conclusion that turfgrass is a good choice for fighting the greenhouse effect.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it adds more information about the benefits of turfgrass. The phrase "In addition to" shows that this paragraph provides extra details that support the previous claim about turfgrass being useful.