军册
参考答案：
是明代控制军士和军户以保障军队兵员补充的文书。
If my lawyer ______ here last Friday, he _____ me from telling the truth.
A．had been; would have prevented
B．had been; would prevent
C．were; would prevent
D．were; would have prevented
已知二次型
，经过正交变换
后可化为
，则a=______，b=______．
，经过正交变换
后可化为
，则a=______，b=______．