(a) That's wrong. The first two statements are both correct. The third statement (c) is incorrect.

When things belonging to different owners are mixed together, ownership of the mixture depends on whether the different parts can be identified and separated, and whether the mixing was done with the consent (express or implied) of the owners of each constituent part.

If the different parts can be identified and separated, then ownership of the various parts does not change.

If the different parts can no longer be identified and separated, and provided that the mixing was done with the consent of the owners, the former owners become co-owners (owners in common), and their ownership is in proportion to their contribution.

If the mixture was made by one owner without the consent of the other, then the mixture belongs solely to the other owner.

Possession is not relevant to deciding ownership of mixtures.