An empty thick conducting shell of inner radius $a$ and outer radius $b$ is shown in the figure. It is observed that the inner face of the shell carries a uniform charge density $-\sigma$ and the outer surface carries a uniform charge density $+\sigma$. If a point charge $q_A$ is placed at the center and another point charge $q_B$ is placed at a distance $c (> b)$ from the center of the shell,then choose the correct statement.

• A
  The force experienced by charge $q_A$ is $\frac{\sigma q_A b^2}{\varepsilon_0 c^2}$.
• B
  The force experienced by charge $q_A$ is zero.
• C
  The force experienced by charge $q_B$ is $\frac{\sigma q_B b^2}{\varepsilon_0 c^2}$.
• D
  The force experienced by charge $q_B$ is $\frac{k q_A q_B}{c^2}$.