Fact 1: Antigens are found on cancer cells and the cells of transplanted organs.

Fact 2: Antigens can be any molecule that causes antibody production.

Given the two facts above, answer the question "A molecule that causes antibody production is found on what?" with the following options: 
- solid, liquid, gas
 - organs
 - Epidermis
 - aqueous solution
 - the skin
 - animals
 - cancer cells
 - humans


 

       cancer cells  