[译] 那个年轻人留了一头长发。
[误] The young man has long hairs.

[正] The young man has long hair.
[注] hair 是集合名词，没有复数形式。只有在表示具体的一根根毛发时，hair 才用作可数名词，有复数形式。如：Although young, he has had several grey hairs. 尽管年轻，他已长出了几根白发。