First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of deserts. It gives a clear definition of what deserts are. This follows the rule of Topic Sentence. It does not need any other sentence for context. Why other lines are not chosen? Paragraph 2 starts with 'They', which is a pronoun. This means it needs more context. Paragraph 3 starts with 'Because', which is a conjunction. It cannot stand alone. Paragraph 4 starts with 'Any', which is also a pronoun. It needs more information to be clear.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the ideas about deserts and their life forms. It gives a conclusion about how plants and animals survive in deserts. This follows the rule of Summary Style.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it gives more details about deserts. It uses the Connector strategy. The second sentence explains the temperature of deserts, which follows the definition in the first sentence.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it explains the effect of the temperature on biodiversity. This follows the Cause and Effect Relationship rule. The extreme conditions mentioned in Paragraph 2 lead to less biodiversity, as stated in Paragraph 3.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it talks about how plants and animals adapt to the conditions mentioned in Paragraph 3. This follows the Logical Order rule. The lack of biodiversity leads to the need for special adaptations.