A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the topic of biology. It gives a clear definition of the word 'biology' and shows its origin. This follows the rule of Topic Sentence because it sets up the main topic without going into details. Why other lines are not chosen? Paragraph 2 starts with 'It is defined...' which uses a pronoun and does not stand alone. Paragraph 3 starts with 'Classification and behavior...' which is specific and does not introduce the topic. Paragraph 4 starts with 'It also studies...' which also uses a pronoun and refers back to the topic.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the topic of biology. It gives a final idea about what biology studies. This follows the rule of Summary Style because it brings together the earlier points about biology.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): This pair connects because Paragraph 2 explains what biology is. It follows the Broader to Specific Strategy. The first paragraph gives a general idea, and the second paragraph gives more details about biology.
• Pair 2 (Paragraph 2 → Paragraph 3): This pair connects because Paragraph 3 talks about a specific part of biology. It follows the Logical Order rule. The second paragraph gives a definition, and the third paragraph gives an example of what biology studies.
• Pair 3 (Paragraph 3 → Paragraph 4): This pair connects because Paragraph 4 continues the discussion about biology. It follows the Logical Order rule. The third paragraph talks about classification, and the fourth paragraph adds more information about what biology studies.