Which of the following best describes a cell?

The correct choice is based on the definition of a cell as the fundamental building block of all living organisms. Cells are considered the basic unit of life because they carry out essential life processes, such as metabolism, growth, and reproduction. Every living organism, from the simplest bacteria to complex multicellular organisms like humans, is made up of cells, which perform specific functions necessary for the organism's survival.

In contrast, a complex organism refers to a fully developed entity made up of many cells, tissues, and organs. A type of tissue is a group of similar cells working together to perform a specific function, highlighting that tissues are a higher organizational level than cells. A group of organs refers to systems within an organism, such as the digestive or respiratory system, which are made up of different tissues and cells. Thus, understanding that a cell is the most fundamental unit gives clarity to why it is correctly identified as the basic unit of life.