First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic. It talks about the organization and the number of tree species. This is a broad overview of what the text will discuss. It does not use any pronouns or definite articles that need prior context. Why other lines are not chosen? Paragraph 2 starts with "The researchers" which uses a definite article and assumes prior knowledge. Paragraph 3 starts with "BGCI" which is also a specific reference. Paragraph 4 starts with "Of that number" which refers back to previous information. All these do not stand alone.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it summarizes the findings and gives a conclusion about the data. It reflects on the main topic and shows the importance of the information presented.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): This pair connects because the second paragraph gives more details about the organization mentioned in the first paragraph. It explains how the researchers collected information, which is a logical continuation of the topic.
• Pair 2 (Paragraph 2 → Paragraph 3): This pair connects because the third paragraph provides the results of the research mentioned in the second paragraph. It shows what the researchers found, which is a logical order of information.
• Pair 3 (Paragraph 3 → Paragraph 4): This pair connects because the fourth paragraph gives more details about the findings in the third paragraph. It explains the implications of the number of species identified, which shows a cause and effect relationship.