Point charges +4q, -q and +4q are kept on the x-axis at points $\mathrm{x}=0, \mathrm{x}=\mathrm{a}\text{ and }\mathrm{x}=2\mathrm{a}$ respectively, then

• A

  Only q is in stable equilibrium

• B

  None of the charges are in equilibrium

• C

  All the charges are in unstable equilibrium

• D

  All the charges are in stable equilibrium