单项选择题

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
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单项选择题
Many new ______ will be opened up in the future for those with a university education.
A．opportunities
B．necessities
C．realities
D．probabilities
单项选择题
Mrs. Brown is supposed ______ for Italy last week.
A．to have left
B．to be leaving
C．to leave
D．to have been left
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