Which nation has finally opened its borders to fully vaccinated international travelers after 20 months?

A. US 

B. Australia

C. Japan

D. China

Explanation:

The United States opened its land and air borders to international travelers fully vaccinated against COVID-19 from November 8, 2021, after almost 20 months of travel restrictions. With this, US has largely opened up widely for foreign visitors although some states still have local restrictions like mask mandates and vaccine requirements.