问题
单项选择题
Control of flooding should be addressed（）.
A.first
B.following control of fire
C.following restoration of vital services
D.only if a threat exists
答案
参考答案：B
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Control of flooding should be addressed（）.
A.first
B.following control of fire
C.following restoration of vital services
D.only if a threat exists
参考答案：B
，若f（a）=2，则实数a=（）．