Complete the sentences to describe the different levels of organization in living things. A/An is a group of organs that work together to perform a common function. A/An is a group of tissues that work together to perform a common function. A/An is a group of organ systems that work together to perform a common function. A/An is a basic unit of structure and function of all living things. A/An is a group of cells that work together to perform a common function.