单项选择题

Recent studies have identified four major global environmental risks; acid rain, ozone depletion, deforestation and the greenhouse effect（）

A. recognized
B. proved
C. got rid of
D. multiplied

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单项选择题

Professor Jeffrey's lecture on the recycling of waste paper and other garbage will show（）can still be improved．

A．that the municipal authorities have done
B．how those the municipal authorities have done
C．how what the municipal authorities have done
D．that how the municipal authorities have done

单项选择题

All the references she has obtained for her doctoral dissertation（）about twenty items．

A．make up for
B．add up to
C．come up with
D．put up with