Overview. If you frequently experience shortness of breath or you hear a whistling or wheezy sound in your chest when you breathe, you may have asthma â a chronic condition that causes inflammation and narrowing of the bronchial tubes, the passageways that allow air to enter and leave the lungs.
1 At 47,958 kilometres (29,800 miles) in total length, the Pan-American Highway is the longest road in the world.  The road starts in Alaska, North America and ends in the lower reaches of South America.
World's longest, largest, busiest highways. The United States has the largest national highway system. Click NEXT to read more... Image: An aerial photograph shows traffic on the southern portion of the 18-Mile Stretch, a facet of U.S. Highway 1 that connects South Florida with the Florida Keys in Key Largo, Florida. Photographs: Andy Newman/Reuters. World's longest, largest, busiest highways. China's highway network is the second most extensive in the world, with a total length of about 3.573 million km.