A medical researcher has isolated a chemical from cigarette smoke. When the scientist mixes a small amount of the substance with living human cells, the chemical damages unsaturated fatty acids in the cells' plasma membranes. He is able to prevent this damage by adding vitamin E to the mixture of the chemical and cells. Based on this information, the scientist has . determined that the chemical in cigarette smoke is an oxidizing agent discovered a vitamin-based cure for lung cancer conducted an in vitro experiment under poorly controlled conditions identified vitamin E as a prooxidant