First sentence: Why this is the first line? This paragraph is the first line because it introduces the main topic of urban geography and Carl Sauer's influence. It sets the stage for the discussion about urban geography. It does not refer to any previous information, making it independent. Why other lines are not chosen? Paragraph 2 starts with "Throughout the 1950s and 1970s," which is a time reference that needs context. Paragraph 3 starts with "At the same time," which refers back to earlier information. Paragraph 4 starts with "Using this data," which also needs prior context. Paragraph 5 starts with "By the 1970s," which again needs earlier information to make sense.

Concluding sentence: Why this is the last line? This paragraph is the last line because it wraps up the discussion about urban geography. It summarizes the main point that urban studies became very important by the 1970s. It uses conclusive words to show the end of the topic.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it shows the development of geography after Carl Sauer's influence. It uses the Connector strategy by starting with a time reference that shows the progression of ideas.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it continues the idea of using quantitative methods in geography. It uses the Logical Order strategy as it shows how urban geographers applied these methods.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it explains what urban geographers did with the quantitative information. It uses the Cause and Effect Relationship strategy, showing how the use of data led to comparative studies.
• Pair 4 (Paragraph 4 → Paragraph 5): Paragraph 5 connects to Paragraph 4 because it summarizes the outcome of the studies mentioned in Paragraph 4. It uses the Broader to Specific strategy, showing how the studies led to urban studies becoming the main focus.