单项选择题

There is supposed to be a safety （）which makes it impossible for trains to collide.

A．appliance
B．accessory
C．machine
D．mechanism

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单项选择题
The elderly Russians find it hard to live on their state（）

A．pensions
B．earnings
C．salaries
D．donations
单项选择题
The （）on this apartment expires in a year's time.

A．treaty
B．lease
C．engagement
D．subsidy
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