题目内容：
A new technique （ ）, the yields as a whole increased by 20 per cent.
A．working out B．having worked out
C．having been worked out
D．to have been worked out
参考答案：
答案解析：
单选题：A new technique （ ）, the yields as a whole increased by 20
- 题目分类：公共英语四级
- 题目类型：单选题
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B．having worked out
C．having been worked out
D．to have been worked out