68. 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

热心网友

A 这是语感 念书多了就有这种感觉 抱歉 具体的我不是很清楚 不过我敢肯定就是这个答案

热心网友

agree