采用无缝钢管制造的压力容器的公称直径指的是管道的()
A、内径
B、外径
C、中径
D、不是内径也不是外径
参考答案:B
When his wife died, he lived ______; his lovely pet dog made him feel less ______.
A.alone, alone
B.lonely; alone
C.lonely; lonely
D.alone; lonely
砾石挡火器是为了保障制氢系统安全而设的,如果气体出口着火,挡火器可以阻止火焰蔓延到系统内部。