Right now in China, talks on the street have been about the strange weather and it's raising a lot of concerns. A heavy haze  has blanketed many cities in the northern and southern parts of the country in part of an unusual weather system that's descended on the nation. The haze stretches over a vast area, from Hebei and Shan-dong Provinces in the north all the way to Zhejiang, Anhui, Jiangsu, Hunan and Fujian provinces in the south. At its worst, the smog is reducing visibility to less than 200 meters and disrupting traffic, both on the ground and in the air. The weather front has also led many to worry about the possible health impacts. Many cities are waking up to another day covered by a dense haze. In Beijing, drivers have to keep their lights on even though it's already past eight o'clock in the morning. Even driving at very slow speeds, the roads can still be very dangerous. In some of the worst hit areas, drivers can't even tell the colors of traffic signals. Authorities have stepped in to close off many highways across the troubled region. In Shandong Province, the highways that are open are backed up for miles. And traffic police have stepped up their patrols. In the region's airports, flights information boards have gone red. A huge number of flights have been delayed or cancelled, nearly three hundred in Beijing alone, leaving thousands of passengers stranded. Some are more frustrated than impatient. Passenger from Jinan airport, Shangdong province, said: "I've been waiting for more than five hours. It's Mother Nature, so there's really nothing we can do." The airport is urging passengers to confirm with their carrier whether their flight will still take off as scheduled. Back on the city streets, people are wearing breathing masks to get free from any ill effects. Fog has cleared a little in Shanghai. But damage has already been done. Shanghai resident said: "I've been wearing the mask, but still, my throat feels sour and itchy. I think it's because of the weather." The weather forecast predicts a cold front is about to sweep across central and eastern China tomorrow. Many are hoping that this will clear away the depressive haze as well as the harm it brings. The passage is developed by  _  .
making comparisons giving examples following the time order analyzing the causes