Two gases $X$ (molecular weight $M_{X}$) and $Y$ (molecular weight $M_{Y}$; $M_{Y} > M_{X}$) are at the same temperature $T$ in two different containers. Their root mean square velocities are $C_{X}$ and $C_{Y}$ respectively. If the average kinetic energies per molecule of two gases $X$ and $Y$ are $E_{X}$ and $E_{Y}$ respectively, then which of the following relation$(s)$ is(are) true?

• A
  $E_{X} > E_{Y}$
• B
  $C_{X} > C_{Y}$
• C
  $E_{X} = E_{Y} = (3 / 2) R T$
• D
  $E_{X} = E_{Y} = (3 / 2) k_{B} T$