Tourists visit Qianling Mausoleum, a tourist site in Xianyang City, northeast China's Shaanxi Province, Dec. 4, 2014. Some stone sculptures at the site were eroded by biological bacteria. Whether to clear the biological bacteria is still a controversial issue, because the new appearance of the sculptures may impact the cultural relics' sense of history. Qianling Mausoleum is the double tomb of Li Zhi, a Tang Dynasty (618-907) emperor, and his wife, empress Wu Zetian. Wu Zetian was China's only female monarch. (Xinhua/Ding Haitao)