A is the only one I can see here that would apply only to an octopus.
Obviously, an octopus is capable of complex and rapid movement. It has tentacles, it can jet itself backward in the water very fast, and it is an intelligent animal. Sunflowers do not have such movement.
The sunflower would be the organism with rigid cell walls, as all plants have. Animals of any kind do not have these walls, so B is out.
Choanocytes are not found within either species, but you should check me on this one. Sponges and related, primitive sea life have these cells, also called "collar cells" , and they have flagella which beat to create a current through the sponge to bring in food and remove wastes. I think that the octopus is too advanced for this, but again, you should check me. I know for sure that sunflowers do not have collar cells. Unless the octopus has collar cells, which I do not think it does, C is out.
There are no terrestrial octopus species. If there are aquatic sunflowers, fine...botany is not my area..but your question asked what only the octopus has, and there are no terrestrial octopus species so D is out.
