Have you ever visited Longmen Grottoes (龙门石窟 ) or Yungang Grottoes? Around 1, 800 years ago, Chinese artists (create) grotto statues (雕像) in mountains. Over the years, these statues have been through earthquakes, floods and wars. Now the 21st century, however, they are facing an even (big) danger: tourism. Too many tourists go to visit those grottoes every year and this (certain) does harm to the grotto statues. Do you know how?
According to a study, the CO, that visitors breathe out has made the air more acidic(酸性的). Also, visitors bring in microorganisms(微生物). All of these things can be (harm) to the grotto statues.
Behaving badly can cause harm to the grotto statues as well. Too many visitors touch the grotto statues and cause (they) surfaces to change color.
When we visit the grottoes, we can often see a sign saying, "No Flash!" or "No Photos!". This is the strong light can be bad for the statues, especially those with color. The light can make it easy for them to lose their color.
(protect) those ancient cultural treasures, recently China has asked the workers who take care of those grottoes to control number of visitors. And tourists are encouraged to book (ticket) on the Internet and stay away from busy hours when visiting.
