单选题：C　　Food sometimes gets poisoned with harmful things. A perso

C
　　Food sometimes gets poisoned with harmful things. A person who eats such food can get an illness called food poisoning. Food poisoning is usually not serious, but some types are deadly, The symptoms of food poisoning usually begin within hours of eating the poisoned food. Fever is one of the most common symptoms.
　　Certain microorganisms （微生物） cause most types of food poisoning. Bacteria and other microorganisms can poison eggs, meat, vegetables, and many other foods. After entering the body, these tiny living things release （释放） poisons that make people sick.
　　Some chemicals can also cause food poisoning. They are often added to food while it is being grown, processed, or prepaid. For example, many farmers spray chemicals on crops to kill weeds and insects. Some people may have a bad reaction to those chemicals when they eat the crops.
　　Some plants and animals contain natural poisons that are harmful to people. These include certain kinds of seafood, grains, nuts, seeds, beans, and mushrooms.
　　When people handle food properly, the risk of food poisoning is very small Microorganisms multiply rapidly in dirty places and in warm temperatures. This means that people should never touch food with ditty hands or put food on unwashed surfaces. Food should be kept in a refrigerator to stop microorganisms from gnawing. Meat needs to be cooked thoroughly to kill any dangerous microorganisms. People should also wash food covered with chemicals before eating it. Finally, people should not eat raid mushrooms or other foods that grow in the wild. Some of these foods may contain natural materials that are poisonous to humans. In addition, some types of fish can be poisonous.
　　Most people recover from food poisoning after a few days of resting and drinking extra water. If people eat natural poisons, they must go to the hospital right away to have their stomachs emptied.
Food poisoning can be caused by all the following EXCEPT 　　 . A．some chemicals
B．low temperatures
C．some tiny living things
D．certain natural materials