单项选择题

The scientist's work was based on______.

A．occasional observations
B．systematic observations
C．observations of several nests
D．observations of an undisturbed nest
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单项选择题
What is the most suitable word that describes the work of a policeman according to the passage
A．Dangerous.
B．Demanding.
C．Distressing.
D．Dramatic.
单项选择题
A policeman has to be trained in criminal law because______.
A．he must work hard to help reform criminals
B．he must believe as professional lawyers do
C．he must be able to tell when and where a crime is committed
D．he must justify the arrests he makes of criminals
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