先来看一道题：

a. He must be very old. Look, he has grey ________.

b. He found some ________ in his soup.

A. hair, hair B. hairs, hairs C. hair, hairs D. hairs, hair

【分析】此题应选 C, 容易误选 A, 误认为hair永远不可数。其实hair这个词既可以是可数的, 也可以是不可数, 只是含义稍有变化：

1. 作为可数名词, 是指一根一根的"头发"或"毛发"：

Look at this, a hair in my soup. 你瞧, 我的汤里有根头发。

The cat has left her loose hairs all over my clothes. 猫掉的毛弄得我衣服上到处都是。

My father has quite a few gray hairs. 我父亲已有不少白发。

There is not a gray hair on his head. 他头上没有一根白头发。

2. 作为不可数名词"头发"的总称, 是集合名词：

I'll have my hair cut. 我要去理发。

He has blond hair. 他有一头金发。

She has a beautiful head of hair. 她有一头漂亮的头发。

The woman likes to do her hair in foreign style. 这个女人喜欢把头发梳成外国式。

试比较以下句子：

He has grey hair. 他满头白发。

He has grey hairs. 他有些白发了。