Online sales now represent as much as one-tenth of all retail sales in the United States.

目前，网上销售占到了美国零售总额的十分之一。

So there must be at least four rooms, which we can represent as circles, drawing lines between them for the doorways.

所以这至少有4个房间，我们可以把它们绘成圆形，在它们的门之间连线。