Answer: Method of obtaining food and type (and number) of cells.
Explanation: A taxonomy key is used in placing organisms into Kingdom. It is simply a checklist of of characteristic and features that help in determining what group organisms are placed in. Now, two main characteristics scientists use for Kingdom placement is the method of obtaining food and the type and number of cells the organism contains. By this method, organisms are classed into Plants and Animals. Plants because they are adapted to producing their own food from inorganic substances and water and by utilizing light energy in a process called photosynthesis; Animals because they have no way of making their own food, but instead rely on other organisms for their energy provision.
The other method is the type (and number) of cells these organisms contain, in that they are classified into prokaryotic, those lacking a membrane-bound nucleus, mitochondria, or any other membrane-bound organelle and eukaryotic, those with membrane-bound organelle organisms. While eukaryotic organisms can be unicellular or multicellular prokaryotes are not.