Fact 1: Lymphocytes are the key cells involved in the immune response.

Fact 2: Lymphocytes are produced in the bone marrow.

Given the two facts above, answer the question "where are the key cells involved in the immune response made?" with the following options: 
- bloodstream
 - humans
 - mitosis
 - bone marrow
 - organs
 - Epidermis
 - critical organs
 - stomach


 

    bone marrow     