A metric unit is the standard unit used to measure something. A base unit is one of he following seven units: meter (length), kilogram (mass), second (time), ampere (current), kelvin (temperature), mole (amount of substance) and candela (luminosity). They're referred to as the base units as all other metric units can be derived from them.
The base unit for length is the metre.
The meter is the metric base unit for volume, and the cubic meter is the derived unit.
A second is a SI base unit.
The SI, or metric, base unit for length is the metre.
The base unit of mass is the kilogram.
The base unit for length is the metre.
If, by 'metric system', you mean the 'SI system', then there is no base unit for volume. The unit for volume is called a 'derived unit', and it is the cubic metre (m3).
meter
The SI base unit for mass is the kilogram.
In the metric system, meters are the base unit to measure length.
In the SI system, the base unit for temperature is the kevin.
The official system of measurements is the SI; it has SEVEN base units.