表示背景图像apple.gif只在水平方向上平铺的CSS属性定义为（ ）
Abackground-repeat:repeat-x
Bbackground-repeat:repeat-x;
Cbackground-repeat:repeat-y;
Dbg-repeat:repeat-x;
Abackground-repeat:repeat-x
Bbackground-repeat:repeat-x;
Cbackground-repeat:repeat-y;
Dbg-repeat:repeat-x;