常用于锁紧精度要求高且长时间锁紧的液压系统的是（）
A.利用换向阀的中位机能锁紧
B.利用液控单向阀锁紧
C.利用平衡阀锁紧
D.以上都是
参考答案：B
After the new technique was introduced the factory produced ______cars in 1994 as the year before.
A．as twice many
B．as many twice
C．twice as many
D．twice as
已知A是3阶矩阵，A*是A的伴随矩阵，如果矩阵A的特征值是1，2，3，那么矩阵(A*)*的最大特征值是______．
