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

Fact 2: An antigen is a protein that prompts an immune response to cancer cells.

Given the two facts above, answer the question "a protein that prompts an immune response are found where?" with the following options: 
- the skin
 - critical organs
 - epidermis and dermis
 - layers of fat
 - Veins and arteries.
 - at or near the margins
 - Earth orbiting the Sun
 - on cancer cells


 

        on cancer cells 