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 发表: 2005-06-16 22:10:07 人气:5605  
[求助]请教一个语法题！
大家好！
下面的语法题怎么做!
关娜老师的补充资料P9
2、独立主格
1、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
答案是C
按句意是个被动语态
有些不明白为什么have要加ing
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