（三）   Fall has arrived for most countries in the northern sideof the earth. The leaves have begun to change color and itgets colder and colder with each passing day. For Canadians,the coming of fall means that winter is not very far behind.Canadians experience some of the coldest winters in NorthAmerica. The endless blankets of snow paint the world inwhite and are beautiful scenes to many people. However,there is one thing at the back of every Canadian's mindduring winter time: frostbite.   Frostbite is the result of body tissues that becamefrozen and died. When it gets below 0°C outside, the bodystops sending as much blood to the body parts except thevital ones important for life. The fingers, toes, ears and noseget little blood while the heart, lungs and brain get most ofit. Without the blood to keep them warm, they begin tofreeze. Numb fingers and toes are a sign that those areasaren't getting enough blood. Not serious cases can be treatedquite easily at hospitals. Serious cases usually lead toamputation, or cutting off your legs or hands. So, if you everdecide to go to Canada during the winter, make sure youdress very warmly and keep your socks and gloves dry. It'sthe best way to ensure you'll still have your fingers and toeswhen spring returns! tissues 組織；numb 失去知覺的
52. What is the main idea of the reading?
(A) The people in Canada experience the coldest daysin the world.
(B) Keep yourself warm, or you will lose your bodyparts.
(C) Falling snow in the northern side of the earth iswonderful.
(D) It takes no time for winter to come after fall hascome in North America.