单项选择题

Chimpanzees are frequently used as stand-ins for human beings in experiments.

A．partners
B．role-models
C．stand-bys
D．substitute
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单项选择题
One of the most interesting inhabitants of our world is the bee, an insect which is indigenous to all parts of the globe except the Polar Regions.
A．residents
B．pets
C．intimates
D．creatures
单项选择题
When we were in the mountains, we often found ourselves entirely enveloped by the fog.
A．confined
B．surrounded
C．darkened
D．blocked
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