Fact 1: Passive immunity lasts only as long as the antibodies survive in body fluids.

Fact 2: Inside the body, blood is normally a fluid.

Given the two facts above, answer the question "passive immunity lasts only as long as the antibodies survive where?" with the following options: 
- cows
 - heat
 - skin
 - Mitosis
 - blood
 - humans
 - Summer
 - animals


 

     blood    