Which of the Following Is Not a Method Used to Observe

Multiple Choice

Which of the following is not a method used to observe operations in the immune system?

A) Determine the lymphocyte count in a blood draw.
B) Extract blood,add cancerous tumor cells,and measure effectiveness of natural killer cells.
C) Inject a foreign agent in the skin and measure the amount of swelling.
D) Swab the inside of a cheek and measure the level of cortical.