what is the only base unit with a name that contains an SI prefix?

Question

please explain

Answer 1

kilogram, prefix being kilo-.

The kilogram (kg) is the SI base unit of mass, it just so happens that the base unit uses the kilo- prefix indicating that 1 kg = 1000 g, but the gram is not a base unit.

SI base units,
http://physics.nist.gov/cuu/Units/units.html
SI prefixes,
http://physics.nist.gov/cuu/Units/prefixes.html