【Weallknowthatzebrashavestripes（条纹）．Butwhy？It'shardtogetablack-and-whiteanswer．Thisisaquestionnotjustcommonpeoplelikeushaveasked，butscientiststoo．Severalstudieshavebeendonetofindoutthereasonbehind】

　　We all know that zebras have stripes （条纹）．But why？It's hard to get a black-and-white answer．This is a question not just common people like us have asked，but scientists too．

　　Several studies have been done to find out the reason behind the stripes and many theories （理论）have been suggested．According to a recent study，the type of stripes changes depending on the temperature where zebras live．The warmer the place is，the more stripes they may have．From this study，scientists believe that stripes may help to keep a zebra cool in warmer places．

　　According to the cooler temperature theory，when air hits a zebra，the movements of air are stronger and faster over the black parts and slower over the white．This is because black color takes in more heat than white．So at the point where the black and white meet，there is cooling airflow．It can quickly cool a zebra's skin!In fact，scientists have noticed that heavily striped zebras have 5.4T lower skin temperature than other animals without stripes in the same area．

　　Some scientists believe that stripes may be an adaptation （适应）by zebras to defend （防卫） themselves from the horseflies that follow zebras．The cooler temperature theory holdsmerit here too，since disease-carrying flies like horseflies like it hot．Flies also don't like landing on striped surfaces．

　　There also have been many other theories that have been suggested for why zebras have stripes．Some explanations are very common．One of them is that stripes may help zebras hide in grass especially from lions．Lions are color blind and even if they are not far away they may see stripes as grey and be confused by them．What's more，zebras are a large group of animals living together．When a number of zebras stand or move together，stripes may confuse lions into thinking it is one large animal．

　　48．Stripes are helpful for zebras to___．

　　A．stay cool

　　B．move together

　　C．live in cold places

　　D．fight against diseases