问题
选择题
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
答案
答案:C
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
答案:C