A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first line because it introduces the main topic of global health. It is a general statement that does not need other sentences for context. It sets the stage for what follows. Why other lines are not chosen? Paragraph 2 starts with "In their work" which needs context from the first paragraph. Paragraph 3 starts with "They have also forged" which uses a pronoun that refers back to the people in Paragraph 1. Paragraph 4 starts with "For the past seven years" which indicates a time frame that needs prior information.

Concluding sentence: Why this is the last line? This paragraph is the last line because it provides a detailed example of the work done in global health. It wraps up the discussion by showing a specific project that relates to the earlier points about collaboration and expertise.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it gives examples of how the co-directors work in global health. This shows a logical order from the general idea of multidisciplinary activity to specific examples of expertise.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 follows Paragraph 2 because it continues to explain their work. It shows how their expertise leads to relationships with other agencies. This is a logical order of ideas.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it gives a specific example of a collaboration mentioned in Paragraph 3. This shows a clear flow from general relationships to a specific project.