单项选择题

A．when
B．while
C．since
D．then
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单项选择题
In order to reduce the asbestos risk, the report gives the following suggestions except______
A．selecting appropriate type and state of asbestos
B．using wet asbestos instead of dry one
C．using hand tools instead of machine tools
D．working in an open place
单项选择题
Exposure to asbestos fibers is harmful to people's health,______
A．so the use of asbestos is limited
B．but asbestos will continue to be used for a long time to come
C．so other new kinds of materials are under development
D．but they will not be so when ventilation devices are used
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