Final answer:
The SI base unit used to measure mass is the kilogram.
Step-by-step explanation:
The SI base unit used to measure mass is the kilogram. The kilogram is defined as the mass of the International Prototype of the Kilogram, which is a platinum-iridium cylinder kept at the International Bureau of Weights and Measures in France. It is the fundamental unit of mass in the International System of Units (SI).
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