单项选择题

Scientists have spent years into the effects of certain chemicals on the human brain, but with no result.（）

A．studying
B．researching
C．investigating
D．inspecting

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单项选择题
The old worker has been on the （） in this factory for nearly 20 years.

A．pay packet
B．payoff
C．payroll
D．payment
单项选择题
The newspaper did not mention the （） of the damage caused by the fire.

A．range
B．level
C．extent
D．quantity
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