First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of plastic pollution and its effects. It gives a broad overview of the issue 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 "Single-use plastics" which is specific and does not stand alone. Paragraph 3 starts with "This problem" which uses a pronoun and needs context. Paragraph 4 starts with "In recent years" which indicates a time reference and does not introduce the main topic.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion by showing what is being done to solve the problem of plastic pollution. It provides a conclusion to the topic by highlighting efforts to reduce plastic waste.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it explains what contributes to the problem mentioned in Paragraph 1. This follows the Broader to Specific Strategy, where the first paragraph gives a general statement about plastic pollution, and the second paragraph provides specific examples of single-use plastics.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it explains why single-use plastics are a problem. This follows the Cause and Effect Relationship rule, where the second paragraph states the cause (single-use plastics) and the third paragraph explains the effect (non-biodegradability and persistence in the environment).
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it shows what is being done about the problem mentioned in Paragraph 3. This follows the Logical Order rule, where the third paragraph discusses the problem, and the fourth paragraph discusses actions taken to address that problem.