6. In space, a finite set of points $M$ not all lying on the same plane has the property:

For any $A, B \in M$, there exist $C, D \in M$ such that $A B / / C D$.

Then a possible value for the number of points in the set $M$ is ( ).
(A)6
(B) 8
(C) 10
(D) 5
6.C.

As shown in Figure 2, as long as the plane $\alpha$ of the regular hexagon is rotated around one of its diagonals that can serve as an axis of symmetry by an angle $\theta$, four points of the hexagon will be rotated out of plane $\alpha$. These 10 points clearly meet the requirements.