水动力不稳定的原因是()和()两者之间的密度不同。
参考答案:蒸汽;水
One of the tennis rackets broken when they found them.[ ]
A. is
B. are
C. were
D. was
包装容器钢提桶的许可证发证检测,堆码试验的堆码载荷为()N。
A.860
B.1250
C.1380
D.1520