So the quadrilateral MBC 1Q is a parallelogram = = > MQ//BC 1

In the triangle BC 1C, PN//BC 1, so MQ//pn = >; M, n, p, q four-point * * * plane;

It can also be proved that: MQ//RS = > M, Q, R and S four-point * * * plane;

Reconnect AC, A 1C 1, QR//A 1C 1, MN//AC with the midline theorem of triangle.

Because a1c1/AC, QR//Mn = > m, n, q, r four-point * * plane;

So m, n, p, q, r, s six-point * * * surface = = > polygon MNPQRS is a plane figure.