<Solid-2023-240>, hint

Consider a tetrahedron ABCD and M be the midpoint of CD. Draw a point B' on line BM

such that BM=MB'. Then BCB'D is a parallelogram. Suppose a plane # perpendicular to AB'

where B' lie on. Hence the projections of  B,C,D, unto plane # and B' form a parallelogram.