A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic about language and cognitive skills. It does not refer to any previous information. It sets the stage for the discussion about language. This follows the rule of Topic Sentence. Why other lines are not choosen? The other paragraphs are not chosen because they do not stand alone. For example, Paragraph 2 starts with "But" which is a conjunction, so it cannot be first. Paragraph 3 starts with "By contrast" which also shows it is not independent. Paragraph 4 starts with "Because" which shows it needs more context. Paragraph 5 starts with "But" which is also a conjunction.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion. It gives a final thought about language being complex. This follows the Conclusive Words rule, as it contrasts with the previous ideas.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it gives an example of how language is different. This follows the Broader to Specific Strategy. The first paragraph talks about language being unique, and the second paragraph explains how it is universal.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it contrasts the universality of language with other skills. This follows the Contrast rule. It shows that while language is universal, other skills are not.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it explains why language may seem simple. This follows the Cause and Effect Relationship rule. The third paragraph talks about difficulties in other skills, and the fourth paragraph explains the ease of learning language.
• Pair 4 (Paragraph 4 → Paragraph 5): Paragraph 5 connects with Paragraph 4 because it gives a contrasting view. This follows the Contrast rule. The fourth paragraph suggests language is simple, while the fifth paragraph states it is complex.