A:a/b
B:a/2b
C:a/(a+2b)
D:a/(2a+2b)
如图,平面直角坐标系中,直线y=﹣x+a与x、y轴的正半轴分别交于点B和点A,与反比例函数y=﹣3x的图象交于点C,若BA:AC=2:1,则a的值为( )
Air pollution has become ______ than ever before. We must do something to stop it.
化简 ÷ 的结果是( ).
下列词语书写全对的一项是( )