Three blocks $\mathrm{A}$, $\mathrm{B}$ and $\mathrm{C}$ of equal mass $\mathrm{m}$ are placed one over the other on a smooth horizontal ground as shown in the figure. Coefficient of friction between any two blocks is $0.5$. The maximum value of the mass of block $\mathrm{D}$ so that the blocks $\mathrm{A}$, $\mathrm{B}$ and $\mathrm{C}$ move without slipping over each other is

• A

  $\mathrm{6 }\mathrm{m}$
• B

  $\mathrm{5 }\mathrm{m}$
• Correct answer
  C

  $\mathrm{3 }\mathrm{m}$
• D

  $\mathrm{4 }\mathrm{m}$

Hence, the correct answer is option: 'C'.