单选题 A new technique ______, the yields as a whole increased by 20 percent.
A. working out B. having worked out
C. having been worked out D. to have been worked out

【正确答案】 C

【答案解析】本题考分词的独立结构作状语的用法。结合语态，故C项正确。本句大意为：新技术研究出来之后，整个产量增长了20%。