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 undisturbed nests
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单项选择题
It seems that smaller ants perform more of the _______.
A．construction tasks
B．domestic tasks
C．defensive work
D．heavy work
单项选择题
The underlined word good (Para. 3) refers to ants'_______ .
A．co-operation in working
B．sense of responsibility
C．efficiency in working
D．willingness to work hard
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