>>714229946 (OP)It's B or C (where the cube just gets squashed).
Consider what happens moment-to-moment as the portal moves over the cube.
The portal moves over the first layer of atoms. The first layer is now immediately on other other side of the portal.
The portal moves over the second layer of atoms. The second layer is now immediately on the other side of the portal. But wait, there's already something there. So the first layer gets shoved out of the way since the second layer has the rest of the cube and the platform under it (with a bit of resistance due to inertia). Repeat for the rest of the mass.
At the end of the object, it would either get flattened if it wasn't structurally sound enough, or it would have momentum from every layer of particles being forcefully moved repeatedly in a short period of time.