The correct option is (a) allergy.
Explanation:
Allergy is the hypersensitive reaction of a person to some foreign substances coming in contact with or entering the body. The common allergns are dust, pollen mould, spores, fabricates, bacteria, etc. During allergic reaction, there is increased release of histamine from mast cells. Use of anti-histamines and steroids give a quick relief from allergy.
