A father and son learn about how wind power, generated in Zhangbei, Hebei province, is transmitted to Beijing during an exhibition in Beijing on Friday. The exhibition, held at Shougang Park in western Beijing's Shijingshan district, is one of the main highlights marking this year's National Science Popularization Day in China. It is open to the general public from Sept. 16 to 24 and showcases China's latest achievements in various fields of science and technology. [Photo by Yuan Fang/China.org.cn]