The answer is D, algae.
—Evidence—
•] Protozoan definition: a single-celled microscopic animal of a group of phyla of the kingdom Protista, such as an amoeba, flagellate, ciliate, or sporozoan.
•] it does not feature algae, therefore it’s D.
by using rooting harmone roots develop quickly at cutting and and it become more robust than cuttings which don't receive rooting hormone. Cutting harmone is used mostly on ornamental plants in the landscape and to propagate succulents.
It cannot apply on whole plant since it will not mix with old one and a new catergory or plant will develop and it will distroy the originality of the actual plant
Absorb? tell me if im wrong.