To determine the shape of the cross-section made by slicing a right rectangular pyramid (with four equal edges) parallel to the base, we first consider the geometry of the pyramid.
A right rectangular pyramid with four equal edges has a square base, and all the edges connecting the apex to the base corners are of equal length. If a slice is made parallel to the base, the resulting cross-section will also be a square since parallel slicing maintains the shape and proportions of the original base.
Therefore, the correct shape of the cross-section is:
square