The Kilogram Is Currently Defined as

The kilogram is currently defined as

A) the mass of a platinum-iridium cylinder kept in Sévres, France.
B) the weight of a platinum-iridium cylinder as measured on the Earth's moon.
C) the mass of 5.9786332 × 10²⁶ protons.
D) the mass of one liter of pure water, free of air, at standard temperature and pressure.
E) the mass of a cube of pure water, free of air, 10 cm on each side, at standard temperature and pressure.