Two small spheres of masses $M_{1}$ and $M_{2}$ are suspended by weightless insulating threads of lengths $L_{1}$ and $L_{2}$. The spheres carry charges $Q_{1}$ and $Q_{2}$ respectively. The spheres are suspended such that they are in level with one another and the threads are inclined to the vertical at angles of $\theta_{1}$ and $\theta_{2}$ as shown. Which one of the following conditions is essential,if $\theta_{1}=\theta_{2}$?

• A
  $M_{1} \neq M_{2}$,but $Q_{1}=Q_{2}$
• B
  $M_{1}=M_{2}$
• C
  $Q_{1}=Q_{2}$
• D
  $L_{1}=L_{2}$