Four point charges –q , +q +q and-q are placed on y-axis at $\mathrm{r}=-2\mathrm{d},\mathrm{y}=-\mathrm{d},\mathrm{y}=+\mathrm{d}$and $\mathrm{y}=-+2\mathrm{d}$ respectively. The magnitude of the electric field E at a point on the x- axis at $\mathrm{X}=\mathrm{D},\mathrm{with} \mathrm{D}>>\mathrm{d},$, will behave as