A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of light and how we perceive it. It sets up the theme without going into details. This follows the rule of Topic Sentence. Why other lines are not chosen? The other paragraphs do not qualify as the first sentence. For example, Paragraph 2 starts with 'However,' which is a conjunction. Paragraph 3 uses 'With such diversity,' which refers back to something not yet mentioned. Paragraph 4 talks about 'Recent years,' which assumes prior knowledge. Paragraph 5 starts with 'These so-called,' which also refers back to something not yet introduced.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion about new materials in optics. It provides a conclusion about the future of optical technology, following the rule of Conclusive Words.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 using the Connector Strategy. The word 'However' shows a contrast to the idea of light being perceived, expanding on the topic of light by discussing its range.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 follows Paragraph 2 logically using the Broader to Specific Strategy. It takes the broad idea of light's spectrum and connects it to the diverse applications in optics, showing how the topic expands.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 using the Logical Order strategy. It continues the discussion of optics by explaining recent developments in the field, showing a clear progression from the broad applications to specific advancements.
• Pair 4 (Paragraph 4 → Paragraph 5): Paragraph 5 follows Paragraph 4 using the Object Subject Strategy. The 'new materials' mentioned in Paragraph 4 are referred to as 'These so-called metamaterials' in Paragraph 5, showing a clear connection between the two.