To function on their own, unicellular organisms must do what
a. maintain health only
b. get energy, maintain health, and reproduce
c. select a habitat, maintain health, reproduce
d. reproduce and maintain health only

The right answer is Get Energy, Maintain Health, and Reproduce.

Bacteria need the energy to stay alive and reproduce, but the majority are not very demanding in terms of nutrients, they are said to be prototrophic.

A prototroph is a living organism capable of proliferating (living and reproducing) in a basal medium (minimum medium) without requiring the presence of particular growth factors. It synthesizes itself the substances necessary for its proliferation.

The correct answer is (b) Get energy, maintain health and reproduce.

The unicellular organisms must get energy from the food they eat. They  maintain their health and keep on reproducing to ensure their existence on earth. For example an unicellular organism like amoeba carry out digestion to obtain the energy from the food it engulf. The vacuoles present in their body helps to maintain homeostasis (health). The vacuoles only carries waste products out of the body. Amoeba reproduce by the process of binary fission. All the  above mentioned functions are carried by the amoeba to survive on their own.