The answer is (E)- B and C only.
From the very definition of an allergy, we can say that it is an over-reaction or hypersensitivity of the body's immune system towards some foreign bodies (like pollen, medicine, some foods, etc.) that is generally shown by only a few people and not others. Thus option (B) clearly holds true for an allergy.
We know that typical of any allergic reaction is the redness, swelling, itching etc. of the particular area. Actually, allergens, or in simple terms, allergy-causing agents are nothing but antigens. (FYI our body produces antibodies in response to antigens). Lymphocytes in our body produce Immunoglobulin E (IgE), a class of antibodies, as a response to allergens. IgE is anyways found in the body but during severe allergies, there is an over-production of IgE that causes mast cells to release "histamine" that is the main cause of inflammation of the infected area. So the option (C) is true as well.
But mast cells producing platelets and clotting of bronchioles doesn't occur and hence, option (A) doesn't hold true for allergic reactions.