单项选择题

Both tea and coffee contain caffeine, an odorless, colorless ____________ that is soluble in water and in alcohol.

A．substance
B．material
C．matter
D．object
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单项选择题
I must find someone to act as a (an) ____________ for me during my absence.
A．agent
B．delegate
C．representative
D．deputy
单项选择题
The light bulb in the bathroom burned ____________ and Father put in a new one.
A．off
B．down
C．out
D．away
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