Which of the following is the base SI unit for length in the metric system?

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

Answer: (D)

Verified step by step guidance

1. Understand that the International System of Units (SI) defines base units for fundamental physical quantities, such as length, mass, and time.
2. Recall that the base SI unit for length is the 'meter' (m), which serves as the standard unit from which other length units are derived.
3. Recognize that units like millimeter (mm), centimeter (cm), and kilometer (km) are derived units based on the meter, using prefixes to indicate multiples or fractions of a meter.
4. Identify the prefixes: 'milli-' means 10^{-3}, 'centi-' means 10^{-2}, and 'kilo-' means 10^{3}, all modifying the base unit meter.
5. Conclude that among the options given, the meter (m) is the base SI unit for length, while the others are derived units.