Although allergic reactions are triggered by allergens like pollen and fungi, the actual cause of the symptoms like mucous production and constricted airways is a) the body's immune response. b) the effect of medical treatment. c) the surrounding weather conditions. d) the clogging effect of the allergens.

A) the body's immune response.

Explanation:

Pollen and fungi are natural allergens which may get administered in the body  as a foreign antigen. In response to these foreign antigens the body generates an immune response by producing antibodies. These antibodies fight against antigens so that they cannot harm the body in any way. Therefore, symptoms of fever, production of mucous and constricted airways are the examples of production of antibodies in order to generate immune response.