参考译文：

The Pearl River, an extensiveriver systeminsouthern China, flows through Guangzhou City. Itis China’s third-longestriver, only after theYangtze Riverand theYellow River. The Pearl River Delta (PRD) is one of the most developed regions in China with an area of about 11,000 square kilometers. It is the largest urban area in the world in both size and population.The nine largest cities of PRDhave a combined population of over 57 million.Since the reform and opening up (economic liberalization) was adopted by the Chinese governmentin the late 1970s, the Delta has become one of the leading economic regions and a major manufacturing center of China and the world.