Two bodies $A$ and $B$ of masses $10\, kg$ and $15\, kg$ respectively,kept on a smooth horizontal surface,are tied to the ends of a light string. If $T$ represents the tension in the string when a horizontal force $F = 500\, N$ is applied to $A$ (as shown in figure $I$) and $T'$ is the tension when it is applied to $B$ (figure $II$),then which of the following is true?

• A
  $T = T' = 500\, N$
• B
  $T = T' = 250\, N$
• C
  $T = 200\, N, T' = 300\, N$
• D
  $T = 300\, N, T' = 200\, N$