_________ across the railway, a train hit it.

A．While walking

B．Walking slowly

C．As the little pig walking

D．While the little pig was walking

下列说法正确的是(   )

A．同温同压下，H₂ + Cl₂ = 2HCl在光照和点燃条件的△H不同

B．粗铜精炼时，与电源负极相连的是粗铜

C．船底镶嵌锌块，锌作负极，以防船体被腐蚀

D．天然气、沼气和水煤气分别属于化石能源、可再生能源和一级能源