Which SI unit is most appropriate for a scientist to use when measuring the distance between cities?

• A. kilometer (km)
• B. millimeter (mm)
• C. centimeter (cm)
• D. meter (m)

Answer: (A)

Verified step by step guidance

1. Understand the context of the measurement: the distance between cities is typically large, often spanning several kilometers or more.
2. Recall the SI units of length and their typical scales: millimeter (mm) is 10^{-3} meters, centimeter (cm) is 10^{-2} meters, meter (m) is the base unit, and kilometer (km) is 10^{3} meters.
3. Consider the practicality of each unit for large distances: using millimeters or centimeters would result in very large numbers, making the measurement cumbersome and less intuitive.
4. Recognize that meters are suitable for everyday distances but can still be too small for intercity distances, leading to large numerical values.
5. Conclude that kilometers (km), being 1000 meters, provide a convenient and appropriate scale for measuring distances between cities, balancing precision and readability.