You are presented with the question "where are the key cells involved in the immune response made?" and the following answer choices: 
- bloodstream
 - humans
 - mitosis
 - bone marrow
 - organs
 - Epidermis
 - critical organs
 - stomach

Now knowing that lymphocytes are the key cells involved in the immune response and lymphocytes are produced in the bone marrow, choose the best answer.


 

    bone marrow     