物质的下列用途中,是根据物质的物理性质确定的是( )
A:氮气和氩气作灯泡的保护气
B:食品充氮防腐
C:充有氖气的灯管通电时发出红光
D:用氧气炼钢
The farmer is very busy because he's so _______ sheep to keep and so ______ work to do every day.
____
读大洲大洋图分析