A sign notifying customers to wear face masks is seen at the Frankfurt Christmas Market in Frankfurt, Germany, Nov. 22, 2021.Photo:Xinhua

A hand sanitizer is seen next to a booth at the Frankfurt Christmas Market in Frankfurt, Germany, Nov. 22, 2021.Photo:Xinhua

People visit the Frankfurt Christmas Market in Frankfurt, Germany, Nov. 22, 2021.Photo:Xinhua

Photo taken on Nov. 22, 2021 shows a view of the Frankfurt Christmas Market in Frankfurt, Germany.Photo:Xinhua

A girl with a face mask rides on a mini train at the Frankfurt Christmas Market in Frankfurt, Germany, Nov. 22, 2021.Photo:Xinhua

A woman with a face mask selects dessert at the Frankfurt Christmas Market in Frankfurt, Germany, Nov. 22, 2021.Photo:Xinhua