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。