Undercooked beans are suspected of causing the poisoning of 248 students in southwest China, state media reported Friday. Xinhua News Agency said the high school students became sick after eating a school lunch in Yunnan province Thursday. It said investigators suspected the students ate undercooked beans. Most of the students were under observation at four local hospitals, but none of the cases were critical, Xinhua said. Because of lax health standards and poor preparation methods, mass poisonings are common in China.