A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of experimental evidence in social sciences. It does not refer to any previous information and sets the stage for the discussion. This follows the rule of Topic Sentence. Why other lines are not chosen? The other paragraphs are not chosen because they do not stand alone. For example, Paragraph 2 starts with 'In fact,' which is a conjunction. Paragraph 3 starts with 'An apparent example,' which is not general enough. Paragraph 4 starts with 'And,' which is also a conjunction. Paragraph 5 starts with 'But,' which is a conjunction too. Paragraph 6 starts with 'This loss of interest,' which refers back to previous ideas.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it summarizes the main points and explains why interest waned. It brings together the earlier points about the trials and their outcomes, following the Summary Style rule.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it gives more detail about the topic introduced in Paragraph 1. This follows the Broader to Specific Strategy.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it provides a specific example of random allocation mentioned in Paragraph 2. This follows the Topic Example Strategy.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it continues the discussion about randomised trials, showing their development in social work. This follows the Logical Order Strategy.
• Pair 4 (Paragraph 4 → Paragraph 5): Paragraph 5 connects with Paragraph 4 because it shows a change in attitude towards the trials mentioned in Paragraph 4. This follows the Contrast Strategy.