First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic about female humming birds. It does not need another sentence for context. It talks about flashy feathers, which is the main idea. Why other lines are not chosen? Paragraph 2 starts with "They" which is a pronoun and needs context. Paragraph 3 starts with "But" which is a conjunction and cannot be first. Paragraph 4 starts with "Therefore" which is also a conjunction and needs prior information.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the ideas. It uses the word "Therefore" which shows it is a conclusion. It connects all the points made before about colors and their effects.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): This pair connects because Paragraph 2 gives more detail about the female humming birds. It follows the Broader to Specific Strategy, where the first paragraph talks about flashy feathers and the second gives specific information about their color.
• Pair 2 (Paragraph 2 → Paragraph 3): This pair connects because Paragraph 3 explains why the bright blue color may not be important. It uses the Logical Order strategy, where the second paragraph gives a fact and the third explains a problem with that fact.
• Pair 3 (Paragraph 3 → Paragraph 4): This pair connects because Paragraph 4 gives a conclusion about the bright colors. It uses the Cause and Effect Relationship strategy, where the third paragraph talks about mate choice and the fourth explains how bright colors help in another way.