名词hair作复数时后面加s吗？

不加s啊

hair没有单复数之分，所以不用加s

看是做可数还是不可数。
eg：

(a) [C] one of the fine thread-like strands that grow from the skin of people and animals （人或动物的）毛发（指单根）: two blonde hairs on his coat collar 留在他外衣领子上的金发女子的两根头发 * There's a hair in my soup. 我的汤里有根毛. (b)

[U] mass of these, esp on the human head 毛发; （尤指）头发: have one's `hair cut 理发 * have long, black hair 长着一头长、 黑发 * a cat with a fine coat of hair 长着一身好毛的猫. (c) [C] thread-like growth on the stems and leaves of some plants （某些植物的茎和叶上长的）茸毛.

不可数名词复数不加S