The monsoon climate in China can easily bring all kinds of disastrous weather. Since the autumn of 2009, Yunnan, Guangxi, Guizhou and other places in southwest China have suffered from a once-in-a-century drought.

The seasonal distribution of water resources in China is unbalanced, which varies greatly from year to year. It is necessary to build a reservoir to store water in flood season and release water in dry season, so as to adjust the river flow in each season. After the founding of New China, a large number of reservoirs have been built in China to regulate water quantity, improve flood control and drought resistance, and expand irrigation area. Xiaolangdi Reservoir is the largest water control project on the main stream of the Yellow River. After the completion of the Three Gorges Project on the main stream of the Yangtze River, it will become the largest reservoir in China. It can increase the temporal and spatial distribution of water-saving resources to a certain extent. However, with the growth of population, the promotion of urbanization and the development of industry and agriculture, the contradiction between supply and demand of water resources in China is still very serious.

Therefore, choose: d.