你想问农场里有多少牛,你应该对妈妈说:______
A:Mum, How many cows at the farm?
B:Mum, How much cows at the farm?
如图,点A在双曲线上,且OA=4,过A作AC⊥轴,垂足为C,OA的垂直平分线交OC于B,则△ABC的周长为 ( )