Fact 1: Antibodies are large, Y-shaped proteins that recognize and bind to antigens.

Fact 2: Allergic reactions are caused by substances called antigens.

Given the two facts above, answer the question "Allergic reactions can be caused by" with the following options: 
- animals
 - smoking pipes
 - Sulfur dioxide
 - Chemical energy
 - fur and fat
 - antibodies
 - smoking tobacco
 - Pesticides


 

      antibodies   