若x=-1是方程x2-2kx-5=0的解，则k=______．
把x=-1代入方程得到：1+2k-5=0，解得：k=2．
I________the wonderful 2010 World Cup Finals live on TV，but this summer vacation I missed it.[ ]
A．could have watched
B．might watch
C．must have watched
D．need have watched
一般而言，划分系统风险和非系统风险采用的是情景综合分析法。（）
