单项选择题

Perhaps there is still quite a long way to go______ these researchers can find an answer to the mystery.

A．unless
B．until
C．where
D．before
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单项选择题
The mercury in the thermometer is______ to changes in temperature.
A．sensitive
B．sensible
C．sentimental
D．sensational
单项选择题
No matter how______ a hill may be, it is not necessarily worthless.
A．vacant
B．barren
C．empty
D．hollow
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