The right answer is D) a structure made of two or more tissues functioning together for a common purpose.
An organ is a set of specific tissues capable of performing one or more specific functions. The human body has 78 organs and these organs can be grouped into systems (there are 11 of them) to perform more complex functions. For example, the bronchi and lungs are organs that belong to the respiratory system. Organs are necessary to live in good health and some organs are essential. These are the brain, heart, lungs, kidneys, liver and pancreas.