这句话楼主漏写了一个逗号,故容易引起误判,另外,答案B与答案C相同,估计属笔误,原句应为:A new technique ___ ,the yields as a whole increased by 20 percent.
答案: having been worked out
(having been worked out表被动,having worked out表主动)
说明:A new technique having been worked out,独立主格结构,在句中作原因状语,相当于一个原因状语从句:As a new technique had been worked out,.
译文:由于一项新技术得以解决,总产量增长了20%.