title: Howlong____English?YourEnglishis? 
desc: I don't think yu neend sons.
  A.did you study
  B.are you studing
  C.have you studied
  D.have you been studing
answer: 从这道题目的后一句知道:说话人的意思是强调good,是最终结果,而现在完成时强调的正是结果,它与现在完成进行时的最在区别正在此!
  因此,我选C