I know that-2 (English listening practice)

5. Where is the tallest tree? Astralia? Africa? North America?
A: North America. North America has the tallest tree. It's 100 meters tall.

6. Which has the most countries? Asia? Africa? Europe?
A: Africa. There are fifty-three countries in Africa.

7.  Which city has more people? Mexico City? Sao Paulo?
A: Mexico City. Mexico City has over 23 million people.

8. Which causes more global warming(全球變暖) , cars or cows?
A: cows. It's produce(造成) more greenhouse(溫室效應) gasses than cars,    
     trucks(卡車), and airplanes combined. They produce eight percent of
     all greenhouse gasses.