You are presented with the question "What can recognize cancer cells as foreign to the body?" and the following answer choices: 
- electromagnetic energy
 - viruses
 - the immune system
 - bacteria
 - Allergies
 - Microscope
 - the colon
 - turn to a doctor

Now knowing that antigens are molecules that the immune system recognizes as foreign to the body and antigens are expressed by cancer cells, choose the best answer.


 

   the immune system      