保护层开采后,被解放层的应力和瓦斯压力之间的关系是()。
A、应力增大,压力减小
B、应力增大,压力增大
C、应力减小,压力减小
D、应力减小,压力增大
参考答案:C
______ halfway through the exercise, the teacher changed his mind and collected all our papers.
A.When only being
B.When we were only
C.Being only
D.Having been
实际变压器工作时,( )。
A.存在铁耗,不存在铜耗 B.存在铜耗,不存在铁耗C.铁耗、铜耗均存在 D.铁耗、铜耗均不存在