A special exhibition of bronze tripods of the Shang (1,600 BC-1,046 BC) and Zhou (1,046 BC-221 BC) dynasties was kicked off at the National Museum of China in Beijing on Tuesday, jointly launched by the Shanghai Museum.   Three of the most representative bronze round tripods of the Shang and Zhou dynasties and more than 30 cultural relics were on display, telling the story of the Bronze Age.   The three vessels were gathered and shown to the public in Beijing for the first time. Photos: Li Hao/GT