Which option best defines the term "multicellular"?

The term "multicellular" best refers to organisms that are composed of many cells, hence "many units." In biological terminology, multicellular organisms, such as humans, plants, and animals, are made up of multiple cells that work together to perform the functions necessary for life. This stands in contrast to unicellular organisms, which consist of a single cell.

The other options do not accurately capture the biological definition of "multicellular." They either imply a singular nature or a lack of complexity associated with living organisms, making them less relevant in this context. The emphasis on having multiple units is what distinguishes multicellular life from other forms, thereby making the chosen definition most appropriate.