First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic. It tells us that genes are like a manual for cells. This is a broad overview of what the text will discuss. Why other lines are not chosen? Paragraph 2 starts with 'Genes tell' which is not independent because it refers back to the topic of genes. Paragraph 3 starts with 'Scientists now know' which is not independent because it assumes prior knowledge. Paragraph 4 starts with 'Others offer benefits' which is not independent because it refers to previous ideas.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion about mutations. It shows that mutations can have different effects, both good and bad. This gives a complete view of the topic.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): This pair connects because Paragraph 2 explains more about the operating manual mentioned in Paragraph 1. It uses the Broader to Specific Strategy. The first paragraph gives a general idea about genes, and the second paragraph gives specific details about how genes work.
• Pair 2 (Paragraph 2 → Paragraph 3): This pair connects because Paragraph 3 talks about mutations mentioned in Paragraph 2. It uses the Logical Order strategy. The second paragraph explains mutations, and the third paragraph shows what some mutations can cause.
• Pair 3 (Paragraph 3 → Paragraph 4): This pair connects because Paragraph 4 gives more information about mutations mentioned in Paragraph 3. It uses the Cause and Effect Relationship strategy. The third paragraph talks about mutations causing disease, and the fourth paragraph explains that some mutations can also be good.