string, 細繩

A string is used to ensure that the skirts of female members of the honour guard are in the same height from the ground as they prepare for a welcoming ceremony for Congo Republic President Denis Sassou Nguesso outside the Great Hall of the People in Beijing, China, July 5, 2016. (Photo by Jason Lee/Reuters)
A Look at Life in China
http://avax.news/fact/A_Look_at_Life_in_China_11-07-2016.html