Standing in the main hall of the airport, passengers can easily find the different destinations on the large

electric board _______ which airlines can take them.[ ]

A. on      

B. of      

C. to        

D. by

铁制品锈蚀的过程，实际上是铁与空气中的        和         等发生化学反应的过程。据有关资料报导，世界上每年因腐蚀而报废的金属设备或材料相当于年产量的20%~40%。保护金属资源，人人有责。请写出一条防止铁制品生锈的方法                               。