outstanding cuttings of a cube
equilateral triangle: by choosing the vertices on three edges stemming from a common vertex S and equidistant from S
rectangle: for example by using a plane going through two opposite edges
rhombus: for example by using a plane going through two opposite vertices S and S' and the midpoints of two opposite edges going neither through S nor through S'
square: for example by using a plane parallel to two faces
regular pentagon: impossible! the five sides belong to five of the cube's faces, thus to opposite faces; the pentagon has then two pairs of parallel sides
regular hexagon: the vertices are the midpoints of the six edges not going through two opposite vertices S and S'