an organ an organism a system a tissue
I gave my students this multiple choice question: In humans, digestion begins in the mouth. The complete process of digestion occurs with the help of many different parts of the body. Which term best identifies the parts of the body that carry out the function of digestion?

Only one answer is correct among these 4 choices:
- an organ
- an organism
- a system
- a tissue

Could you tell me which one is correct?

a system