The incidence in Japan of most types of cancer is remarkably low compared to that in North America, especially considering that Japan has a modern life-style, industrial pollution included. The cancer rates, however, for Japanese people who immigrate to North America and adopt the diet of North Americans approximate the higher cancer rates prevalent in North America. If the statements above are true, they provide the most support for which one of the following? ['The staple foods of the Japanese diet contain elements that cure cancer.', 'The stress of life in North America is greater than that of life in Japan and predisposes to cancer.', 'The higher cancer rates of Japanese immigrants to North America are caused by fats in the North American diet.', 'The relatively low rate of cancer among people in Japan does not result from a high frequency of a protective genetic trait among Japanese people.']