Fact 1: Plasma cells are activated B cells that secrete antibodies.

Fact 2: Antibodies are protein molecules.

Given the two facts above, answer the question "Plasma cells are activated B cells that secrete what?" with the following options: 
- heat or cold
 - harmful substances
 - Leptospirosis
 - bioaerosols
 - protein molecules
 - Chemical energy
 - major threat to health
 - Veins and arteries.


 

     protein molecules    