Answer:
Cell, tissue, organ, organ system.
Explanation:
Cell is the structural and function unit of the living system. All living organisms are made of cell. Two main types of organisms are unicellular organism and multicellular organism.
Cell is the smallest unit. Cell will combine together and perform a unique function known as tissue. Similar tissue combine together to form a particular organs. Different organs combine together to form the organ system in the living organism.
Thus, the correct answer is option (b).