The correct answer is (d). B cells and T cells are a type of white blood cell that are part of the body’s immune system. They help to protect the body from diseases caused by pathogens, such as bacteria, viruses, and parasites. B cells produce antibodies, which are proteins that bind to specific antigens on the surface of pathogens. This helps to mark the pathogens for destruction by other immune cells. T cells also help to destroy pathogens, but they do so in a different way. T cells recognize and kill cells that have been infected by pathogens, or that have become cancerous.
(a) is incorrect because B cells and T cells do not protect the body from environmental allergens. Allergies are caused by a reaction of the immune system to a harmless substance, such as pollen or dust mites. B cells and T cells do not play a role in this reaction.
(b) is incorrect because B cells and T cells do not alleviate the body’s pain and inflammation. Pain and inflammation are caused by the release of chemicals from damaged tissues. B cells and T cells do not produce these chemicals.
(c) is incorrect because B cells and T cells do not act as immunosuppressants in the body. Immunosuppressants are drugs that suppress the immune system. B cells and T cells are part of the immune system, so they would not be able to suppress themselves.