单项选择题

乙醚(二乙基醚) ( )

A．17
B．20
C．21
D．22
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单项选择题
The ______ contract is a contract between a party who agrees to accept the risk and a party seeking protection from the risk.
A．payment
B．production
C．shipment
D．insurance
单项选择题
Our business has been slack ______ three months.
A．in
B．within
C．over
D．for
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