Concept:Amoeba and Euglena are unicellular organisms, so their body organization is at the simplest living level.Explanation:Unicellular organisms consist of a single cell.That one cell carries out all life processes such as feeding, movement, and reproduction.Tissues, organs, and systems are formed only when many cells work together in multicellular organisms.Since Amoeba and Euglena do not form tissues or organs, their level of organization is the cell.Answer:C. cell