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A new technique ____ out, the yields (收成) increased by 20% .

A. having working        B. having been working 

C. has worked            D. had been worked

A new technique ____ out, the yields (收成) increased by 20% .

A. having working        B. having been working 

C. has worked            D. had been worked

A new technique ____ out, the yields (收成) increased by 20% .

A. having working        B. having been working 

C. has worked            D. had been worked

A new technique ____ out, the yields (收成) increased by 20% .

A. having working　　　　 B. having been working

C. has worked　　　　　 D. had been worked