单项选择题

According the experts, when headset sound reaches 110 decibcls, it can be used at most for ______.

A．one hour
B．half an hour
C．two hours
D．three hours
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单项选择题
At the level of 115 decibels, permanent hearing damage can occur after just ______.
A．15 minutes
B．60 minutes
C．100 minutes
D．105 minutes
单项选择题
We were asked to ______ our essay in three days.
A．hand over
B．hand out
C．hand in
D．hand down
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