First of all, from the front view and the top view, we can get the diagonal with one side being a cube.

As can be seen from the side view, one side is behind the diagonal, perpendicular to the projection of the diagonal on the right, while from the front view and top view, this side must be on the right, that is, a diagonal on the right.

At this time, two sides and four vertices have been found, which is enough as the vertices of tetrahedron, and then connecting the unconnected vertices is a tetrahedron.

Finally, regression verifies the three views.

Then, according to some vertical characteristics of the cube, it is good to choose the one with large bottom area and high calculation.