The specific heat $C$ of a solid at low temperature shows temperature dependence according to the relation $C = D T^{3}$, where $D$ is a constant and $T$ is the temperature in Kelvin. $A$ piece of this solid of mass $m \ kg$ is taken and its temperature is raised from $20 \ K$ to $30 \ K$. The amount of heat required in the process in energy units is

• A
  $5 \times 10^{4} D m$
• B
  $(33 / 4) \times 10^{4} D m$
• C
  $(65 / 4) \times 10^{4} D m$
• D
  $(5 / 4) \times 10^{4} D m$