Right choice is (a) IgE
To explain I would say: Allergies are caused by a hypersensitivity reaction of the antibody class IgE which are located on mast cells in the tissues and basophils in the blood. When an allergen is encountered, it binds to IgE, which excessively activates the mast cells or basophils, leading them to release massive amounts of histamines. These histamines lead to inflammatory responses ranging from a runny nose to anaphylactic shock.