Electric Charges and Fields

Two particles (free to move) with charges +q and +4q are a distance L apart. A third charge is placed so that the entire system is in equilibrium.
A cube has sides of length L. It is placed with one corner at the origin as shown in figure. The electric field is uniform and given by $$\vec{E} = - B\widehat{i} + C\widehat{j} - D\widehat{k}$$, where B, C and D are positive constants.
An electric dipole is placed at a distance x from centre O on the axis of a charged ring of radius R and charge Q uniformly distributed over it.
Which of the follwing does not belong to the group formed by the others?
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