Beijing District Orders Mass Virus Testing Ahead Of Olympics

Chinese authorities are conducting mass COVID-19 testing for 2 million residents in Beijing due to new cases. High-risk residents are advised not to leave the city. The Olympics are being held in a controlled environment, requiring athletes to be vaccinated or quarantined. In Xi'an, a month-long lockdown affecting 13 million people has been lifted.

What is the significance of the term 'bubble' in the context of the Olympics?

Describe the situation in Xi'an regarding the lockdown.