A is a unicellular or multicellular organism that is heterotropic; feeding off dead organic matter or a parasite, feeding off living organisms; reproduces through spores.

A fungi  is a unicellular or multicellular organism that is heterotropic; feeding off dead organic matter or a parasite, feeding off living organisms; reproduces through spores.

Explanation:

FUNGI -: Fungi can be single-celled organisms or multicellular organisms with a great deal of complexity. They can be found in almost any habitat, but the majority of them reside on land, primarily in soil or plant material, rather than in the sea or fresh water. Decomposers are organisms that live in the soil or on dead plant materials and play a vital part in carbon and other element cycling. Some are plant parasites that cause illnesses such mildews, rusts, scabs, and canker. Fungal diseases in crops can cause a farmer to lose a lot of money. Animals are afflicted by a small number of fungus. Athletes' foot, ringworm, and thrush are examples of human skin diseases.

Fungi play an important part in the breakdown of organic materials and in the cycling and exchange of nutrients in the environment. They've long been utilized as a direct source of human food in the form of mushrooms and truffles, as a bread leavening agent, and in the fermentation of a variety of foods like wine, beer, and soy sauce.

Hence , the answer is fungi.