The Mass of a Deuterium (Diatomic) Molecule Is Roughly the Same

The mass of a deuterium (diatomic) molecule is roughly the same as that of an ordinary helium (monatomic) atom. If deuterium gas is at the same temperature as helium gas, the average kinetic energy of the deuterium molecules is

A) larger than the average kinetic energy of the helium atoms.
B) approximately the same as the average kinetic energy of the helium atoms.
C) smaller than the average kinetic energy of the helium atoms.
D) unknown; more information is needed to work out the answer.