Scientists have recently discovered that, in doses massive enough to kill cells, almost any chemical is carcinogenic because cell death causes rapid division among surviving cells, promoting cancer-causing mutations. A few chemicals are also carcinogenic without causing cell death. Until now studies of the carcinogenicity of food additives have always involved administering to test animals doses of additives larger than the largest possible human exposure levels and massive enough to kill large numbers of cells in the animals, and then observing the animals' cancer rates. If the statements above are true, which one of the following conclusions is most strongly supported by them? ['Carcinogenic chemicals are usually absorbed in small doses in the natural environment.', 'Most of the food additives that are now banned because of carcinogenicity could safely be used in human foods.', 'In the doses heretofore used in carcinogenicity studies of food additives, cell death often does not occur in test animals.', 'Until now results of carcinogenicity studies encouraged overestimation of the degree to which some food additives are carcinogenic.']