recently/ UN committee/ report/ world/ oil and gas supplies/ last/ about 100 years/ if/ use/ carefully//

• A. 
  Recently UN committee reported that world's oil and gas supplies, will last about 100 years if they are used carefully.
• B. 
  Recently the UN committee reported that the world's oil and gas supplies would last about 100 years if using carefully.
• C. 
  Recently a UN committee reported that the world's oil and gas supplies would last about 100 years if used carefully.
• D. 
  Recently a UN committee reported that the world's oil and gas supplies would last about 100 years if it was used carefully.