$A$ solid metallic sphere has a charge $+3 Q$. Concentric with this sphere is a conducting spherical shell having charge $-Q$. The radius of the sphere is $A$ and that of the spherical shell is $B$ $(B > A)$. The electric field at a distance $R$ $(A < R < B)$ from the centre is $(\varepsilon_0 = \text{permittivity of vacuum})$

• A
  $\frac{Q}{2 \pi \varepsilon_0 R}$
• B
  $\frac{3Q}{2 \pi \varepsilon_0 R}$
• C
  $\frac{3Q}{4 \pi \varepsilon_0 R^2}$
• D
  $\frac{4Q}{2 \pi \varepsilon_0 R^2}$