本矿开采所造成的采空区、老巷、水窝等积水区,其边界位置准确,水压不超过1MPa,探水线至积水区的最小距离是怎么规定的?
参考答案:
探水线至积水区的最小距离不小于30m。
设—元二次方程x2-2x-4=0的两个实根为x1和x2,则下列结论正确的是( )
A.x1+x2=2
B.x1+x2=-4
C.x1·x2=-2
D.x1·x2=4
Which of the following choices best describes the role of taxes on the after-tax cost of capital in the U. S. from the different capital sourcesCommon equity Preferred equity Debt()①A. No effectDecrease Decrease ②B. DecreaseDecrease No effect ③C. No effectNo effect Decrease
A. ①
B. ②
C. ③