“文明是最美的风景。”下列反映这一公益广告词的行为是( )
A:在食堂随意插队打饭
B:上学回家路上闯红灯
C:随意乱扔零食包装盒
D:轻声有序地上下楼梯
The maths problem is very easy, so I can work it out ________.