求a，b；
参考答案：设特征向量[*] [*] 解得λ=10，a=2，b=5．
※ [27～28] .
. (4 )
A．.
B．.
C． .
D．
After an explosion，repair of emergency machinery and services should be accomplished（）.
A.after control of fire，flooding，and structural repairs
B.immediately，before the emergency is under control
C.after control of fire，but before control of flooding
D.after stability is restored
