Milk rounds are threatened as customers switch to buying from supermarkets.是什么意思？

Milk rounds are threatened as customers switch to buying from supermarkets.

随着顾客转而从超市购买牛奶，送牛奶的生意受到了威胁。

milk

n. 奶，乳液，母乳；vt. 挤奶，榨取；

例句
Soya milk can cause allergic reactions in some children.
有些孩子会对豆浆过敏。

rounds

n. 巡视； <非正>传播，一回合( round的名词复数 )，一连串，阶段，一次射击；

例句
He had only seven rounds of ammunition for the revolver.
他这把左轮手枪只有7梭子子弹。

are

vi. （用于第二人称单复数现在时，第一、三人称复数现在时）是；n. 公亩（等于100平方米）；

例句
We are scared to abandon ourselves to our feelings in case we seem weak or out of control.
我们不敢放纵自己的情感，以免显得太过软弱或缺乏自制。

threatened

adj. 受到威胁的；v. 威胁(threaten的过去分词)；

例句
Union officials made no apologies for the threatened chaos.
工会干部们对于迫在眉睫的混乱局面不予道歉。

as

adv. 同样地，一样地，例如；prep. 作为，以…的身份，如

例句
As far as I can recall, Patti was a Smith.
我记得帕蒂是姓史密斯的。

customers

n. [商业]客户( customer的名词复数 )，主顾，[口]家伙，[计算机]用户；

例句
Have customers been fully apprised of the advantages?...
顾客们已充分了解这些好处吗？

switch

n. 开关，转换，转换器，软鞭子，[信]接线台；vt.& vi. 转变，改变，转换，关闭电流，鞭打；vt. 转换，挥动（棍棒、鞭子等），迅速转动，鞭打；vi. 交换，调换；

例句
What he wants is a switch to a market economy in a way which does not reduce people's standard of living. To many this sounds like wanting to have his cake and eat it.
他想要转型为市场经济,同时又不降低人们的生活水平。在许多人看来,这是想要鱼与熊掌兼得。

to

prep. 向，朝着，到，关于，属于；adv. 朝一个方向的，到某种状态，关闭；

例句
I suggest you leave it to an expert...
我建议你把它留给专家来解决。

buying

n. 购买；v. 购买，购得( buy的现在分词 )，做出牺牲以获得，够支付，买通；

例句
Up to two thirds of 14 to 16 year olds admit to buying drink illegally...
14到16岁的青少年中多达2/3的人承认非法买过酒。

from

prep. （表示时间）从…，（表示原因）因为，（表示来源）来自…，（表示分离）与…分离[隔开]；

例句
...an abortive attempt to prevent the current President from taking office.
企图阻止现任总统连任的失败尝试

supermarkets

n. 超级市场( supermarket的名词复数 )；

例句
Top supermarkets are to ban many genetically modified foods.
大品牌超市即将下架许多转基因食品。