Three copper blocks of masses $M_1, M_2$ and $M_3$ $kg$ respectively are brought into thermal contact until they reach equilibrium. Before contact,they were at temperatures $T_1, T_2, T_3$ $(T_1 > T_3)$. Assuming there is no heat loss to the surroundings,the equilibrium temperature $T$ is ($s$ is the specific heat of copper).

• A
  $T = \frac{T_1 + T_2 + T_3}{3}$
• B
  $T = \frac{M_1 T_1 + M_2 T_2 + M_3 T_3}{M_1 + M_2 + M_3}$
• C
  $T = \frac{M_1 T_1 + M_2 T_2 + M_3 T_3}{3(M_1 + M_2 + M_3)}$
• D
  $T = \frac{M_1 T_1 s + M_2 T_2 s + M_3 T_3 s}{3(M_1 + M_2 + M_3)}$