A.inline-block B.inline C.block D.none
A.width:0;height:0;border:10pxsolidtransparent;border-top-color:#00f; B.width:10px;height:10px;border:10pxsolid#00f;border-top-color:transparent; C.width:0;height:0;border:10pxsolidtransparent;border-bottom-color:#00f; D.width:10px;height:10px;border:0pxsolid#00f;border-bottom-width:10px;
A.background:#ccc,url(bg.png)no-repeat,-100pxcenter; B.background:#cccurl(bg.png)no-repeat-100pxcenter; C.background:#ccc;background-image:url(bg.png)no-repeat-100pxcenter; D.background-color:#ccc;background-image:url(bg.png)no-repeat-100pxcenter;