单项选择题

The basic causes are unknown though certain conditions that may lead to cancer have been（）.

A.conveyed
B.identified
C.notified
D.guaranteed

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A.would not do
B.should not have done
C.should not do
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A.has agreed
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单项选择题No ready technical data available,we managed to（）them.

A.go without
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C.go up
D.go down