learn/ Son/ for/ four years/ English/  so/ he/ the language/ speak/ well

• A. 
  Son was learning the language for four years, so he can speak English quite well.
• B. 
  Son has spoken English for four years, so he learned the language quite well.
• C. 
  So Son has been learning English for four, he can speak the language well.
• D. 
  Son has been learning English for four years, so he can speak the language quite well.