过度包装既浪费资源又污染环境.据测算,如果全国每年减少10%的过度包装纸用量,那么可减排二氧化碳3120000吨,把数3120000用科学记数法表示为( )
A:3.12×105
B:3.12×106
C:31.2×105
D:0.312×107
Shanghai Disney Park will be opened on June 16"'. But the tickets for the first day have sold out.
如图所示,要使灯泡L2发光,必须闭合的开关是( )