The quadruplet sisters Zhu Wanbing, Zhu Wanqing, Zhu Wanyu and Zhu Wanjie are seen in this file picture taken on August 30, 2005, walking hands in hands for their first day in primary school in Nanjing, east China's Jiangsu province. The quardruplet sisters were naturally conceived and born on August 11, 1999 in Nanjing. [Xinhua]