A) This choice is incorrect because a history of frequent dental cavities is not a known risk factor for leukemia.

B) This choice is incorrect because allergies to pollen and pet dander are not associated with an increased risk of leukemia.

C) This choice is incorrect because recurrent urinary tract infections are not known to be a risk factor for leukemia.

D) This choice is correct. Previous treatment with chemotherapy and radiation is a significant risk factor for developing leukemia. Certain chemotherapeutic agents and radiation therapy can damage healthy blood-forming cells in the bone marrow, potentially leading to the development of leukemia later on. This type of leukemia is often referred to as secondary or treatment-related leukemia.