Detailed Instructions: Given a context passage, generate a question from the passage such that its answer is shortest continous span from the passage.
Problem:Wanxian Bridge, or Wanzhou Bridge (simplified Chinese: ; traditional Chinese: ; pinyin: Wanxian Changjiang Daqiao), is a reinforced concrete arch bridge built over the Yangtze River in 1997.
Solution:
What is the surface of Wanxian Bridge made of?