The figure below shows three planes of uniform surface charge density. The sheets of charge density are much larger than the spacing between the sheets. Note: the figure is not to scale. The left and right planes have a surface charge density $+\sigma$ Coulombs per square meter, whereas the center plane has a surface charge density $-2 \sigma$ Coulombs per square meter.
At which of the points A-D in the figure is the electric field equal to zero? Select ALL that apply.