hair在什么情况下是可数名词,什么情况不可数?

hair
n.
1. 毛发;兽毛[C][U][可数与不可数]
The horse has a fine coat of hair.
这匹马长了一身好毛.
2. 头发[U][C][可数与不可数]
There are a few hairs in the book.
书里有几根头发.
3. 些微,一点儿
The ball missed his head by a hair.
球差一点击中他的头.