求解线性方程组的追赶法,要求其系数矩阵为()。
A.三对角矩阵
B.上三角矩阵
C.对称正定矩阵
D.各类大型稀疏矩阵
参考答案：A
Nelson Mandela__________ peacefully at his Johannesburg home on Thursday，President Jacob Zuma said.
A．dies
B．died
C．has died
D．had died
的值是：（）
A.2
B.0
C.1／2
D.1／4
的值是：（）