单项选择题

After years of research, scientists have ______ the virus that is responsible for the disease.

A．recognized
B．identified
C．guaranteed
D．notified
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单项选择题
We can ______ over the ways and means before the construction work starts.
A．reckon
B．speculate
C．ponder
D．presume
单项选择题
The chairman of the board ______ on me the unpleasant job of dismissing good workers the firm can no longer afford to employ.
A．pressed
B．compelled
C．posed
D．tempted
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