hair通常为不可数名词。如果前面加a，a hair表示的是一根毛发的意思。例：He had his hair cut as soon as he got back from varsity.他从大学一回来就剪了头发。Give the hair a quick pull and it comes out by the roots.猛扯头发，头发就会连根拔起。
常见辨析词
Already and All Ready
副词already表示“以前”或“到现在”：
Sasha has already left.
萨沙已经离开了。
短语all ready表示“准备充分的”：
We're all ready to go.
我们已经准备好要出发了。
Altogether and All Together
副词altogether表示“完全地“或“全部地”：
Gus has stopped riding the bus altogether.
格斯再也不开公共汽车了。
短语all together指代人或物集中在一个地方：
The kids sit all together in the back of the bus.
孩子们都坐在公共汽车的后面。
Anyone and Any One
不定代词anyone抽象地指代任何人，而不是某一个人：
Anyone who has an opinion will probably offend someone.
有意见的人很可能会冒犯到别人。
短语any one指代具体但身份不明的物或人：
With enough money, any one of us could be elected mayor.
只要有足够的钱，我们每一个人都能够竞选成为市长。
Awhile and A While
副词awhile表示“一会儿”：
Nico asked me to stay awhile and chat.
尼克让我留下来聊一会儿天。
名词a while表示一段时间：
once in a while people surprise you and rise above self-interest.
有时候，人们会使你感到惊讶，他们抛开了个人利益。
