单项选择题

After years of strenuous work, the scientists are on the __________.of a great discovery of human gene.

A．domain
B．premise
C．threshold
D．pretext
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单项选择题
He was given a gold badge (徽章) as a __________ for his commitment to the development in this field.
A．brim
B．token
C．miniature
D．siege
单项选择题
Some concrete actions were taken to improve the living conditions there but proved to be __________.
A．at a premium
B．to no avail
C．of their own accord
D．on the alert
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