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A．Graduate students.
B．Undergraduate students.
C．Professors.
D．Library employees.
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单项选择题
An operating system is no guarantee of online security probably because ______.
A．some OS suppliers are not trustworthy
B．it still fails to shield users from intrusions
C．antivirus software is not updated in due time
D．some terminals are not installed with such a system
单项选择题
A．It helps improve their safety.B．It allows them to swim faster.C．It helps them fight their predators.D．It allows them to avoid twists and turns.
A．It helps improve their safety.
B．It allows them to swim faster.
C．It helps them fight their predators.
D．It allows them to avoid twists and turns.
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