The heat is flowing through a rod of length $50 \ cm$ and area of cross-section $5 \ cm^2$. Its ends are respectively at $25^\circ C$ and $125^\circ C$. The coefficient of thermal conductivity of the material of the rod is $0.092 \ kcal/m \cdot s \cdot ^\circ C$. The temperature gradient in the rod is

• A
  $2^\circ C/cm$
• B
  $2^\circ C/m$
• C
  $20^\circ C/cm$
• D
  $20^\circ C/m$