This greenhouse gas, often produced by cars and factories, is the main contributor to global warming.
Carbon dioxide (CO₂)
The United States shares its longest land border with this country.
Canada
The Emmy Awards recognize excellence in this field.
Television
This couple starred in Spider-Man: No Way Home and are engaged in real life.
Tom Holland and Zendaya
This year saw the United Kingdom vote to leave the European Union, an event commonly called “Brexit.”
2016
The Great Barrier Reef, located off the coast of Australia, is threatened mainly by this environmental issue.
Coral bleaching
DAILY DOUBLE: This country has the most land borders in the world, sharing borders with 14 other nations.
China
This actor won the Academy Award for Best Actor for his role as Jordan Belfort in The Wolf of Wall Street.
Leonardo DiCaprio
This Friends TV couple, played by Jennifer Aniston and David Schwimmer, had an on-again, off-again relationship.
Rachel and Ross
This year marked the launch of the social media platform Twitter.
2006
Deforestation in this South American country has accelerated, threatening species like jaguars and macaws.
Brazil / the Amazon Rainforest
This river forms part of the natural border between the United States and Mexico.
The Rio Grande
This singer holds the record for the most Grammy wins of all time.
Beyoncé
DAILY DOUBLE: These two stars of Twilight dated in real life and were considered a Hollywood power couple during the 2010s.
Kristen Stewart and Robert Pattinson
In this year, Nelson Mandela was released from prison after 27 years.
1990
This tiny plastic pollutant accumulates in oceans and is consumed by fish and marine animals.
Microplastics
This two countries share the island of Hispaniola in the Caribbean.
Haiti and the Dominican Republic
This movie director won the Academy Award for Best Director for both Schindler’s List and Saving Private Ryan.
Steven Spielberg
This legendary couple starred together in Mr. & Mrs. Smith and were married for over a decade.
Brad Pitt and Angelina Jolie
In this year, the first episodes of Game of Thrones aired on HBO.
2011
This infamous smog event in 1952 caused thousands of deaths in London and led to major air quality reforms.
The Great Smog of London
This African country is completely surrounded by South Africa.
Lesotho
This actor famously refused his Oscar at the 1973 ceremony for The Godfather.

Marlon Brando
This real-life musician couple, both judges on The Voice, are married and occasionally collaborate.

Blake Shelton and Gwen Stefani
In this year, the first human heart transplant was performed by Dr. Christiaan Barnard.
1967