真空试验时,应保持压力18h,其回升压力不超过()方为合格。
参考答案:49MPa
We should go to school at 8:00 _____ school mornings. [ ]
A. at
B. in
C. on
D. of
校大门为()牌楼式建筑
A.六柱五间
B.五柱四间
C.四柱三间
D.三柱两间