According to research by American nutritionists, cauliflower contains indole-indole. Researchers injected a special substance similar to indole in cauliflower into a group of volunteer testers. The efficacy of breast cancer in these subjects. If the following items are true, which of the following can most doubt the above speculation is. ['Low content of indole in cauliflower.', 'Some people who eat cauliflower also have breast cancer.', 'Many people who never eat cauliflower do not develop breast cancer.', 'Estrogen levels are not the only cause of breast cancer.']