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

Fact 2: Furthermore, antibody levels decrease with time.

Given the two facts above, answer the question "Passive immunity decreases with" with the following options: 
- ozone depletion
 - edema
 - passive-aggressive behavior
 - stellar implosion
 - stress
 - HIV
 - time
 - death


 

       time  