Answer:
B. organism
Step-by-step explanation:
A. organ- it's the wrong answer because organs are what make up the organ system.
B. organism- it's the right answer because they contain organ systems. An example includes humans; organisms that have many organ systems like the digestive system and the endocrine system.
C. cell- it's the wrong answer because they are the basic unit of life. They form tissues, which in turn form organs.
D. tissues- it's the wrong answer because they are made up of cells and form organs.