Explanation

• The United States is the world's largest crude oil producing country.

Additional information:

• United States – 18.60 million barrels/day (mb/d)
• Saudi Arabia – 11.01 mb/d
• Russia – 10.50 mb/d
• Canada – 5.29 mb/d
• Iraq – 4–5 mb/d

Last verified on 22-07-2026

Explanation

• Major construction under Qin Dynasty: 1878 (221 to 206 BC)
• Initial wall construction: 7th century BC
• Qin Dynasty ruler: Qin Shi Huang
• Official length (modern survey): 21,196 km
• Ming Great Wall length: 8,851 km

Last verified on 22-07-2026

Explanation

• China is the largest wheat producer in the world.
• USA is among the largest wheat exporters globally due to strong agricultural infrastructure.

Additional information:

1. China: ~135–140 million metric tons
2. India: ~110–117 million metric tons
3. Russia: ~80–90 million metric tons
4. United States: ~45–55 million metric tons
5. European Union: ~130–142 million metric tons (combined)

Last verified on 21-04-2026

Explanation

• First Polio Vaccine Introduced: 1955
• Developer: Dr. Jonas Salk
• Type: Inactivated Polio Vaccine (IPV)
• Oral Polio Vaccine (OPV): 1961
• Developer of OPV: Dr. Albert Sabin

Last verified on 20-07-2026

Explanation

• Country: China
• First use: 806 AD (approx.)
• Early name: Feiqian (Flying Money)
• Dynasty: Tang Dynasty → Song Dynasty (official issue)
• Importance: First-ever paper-based monetary system

Last verified on 11-06-2026