Who can be either an interrogative pronoun ("Who is that?") or a relative pronoun ("The man who sells fruit"). Neither interrogative pronouns (question words) nor relative pronouns (which/that/who and variations) are bound to grammatical number by themselves. The plurality is instead bound to the object in question.
Examples:
"Who is that man?" - singular due to "man"
"Who are those people?" - plural due to "people"
"The man, who is sitting there,..." - again singular due to "man"
"The men, who are sitting there,..." - plural due to "men"
Hair is both countable and uncountable Noun, but it is usually singular when it refers to all the hairs on one's head.
Example:
George has brown hair.
But if it refers to more than one hair, a few hairs, then it takes the plural form and needs a plural verb.
Example:
George has brown hair, but I found a hair on the sofa and suspect he's getting some gray hairs.
When you are talking about specific strands of hair, use the plural form.
Simply put:
Hair can be singular (one hair)
Example:
I found a strand of hair on your sofa. or I found a hair on your sofa
Non-countable singular (when it refers to all the hairs on one's head)
Example:
Shawn has black hair.
Or plural (three hairs, some hairs)
Example:
I Found not one, but three hairs on your sofa.
As Maulik.V said,"To make 'hair' singular, you need to quantify it. So, 'I found a strand of hair on the sofa.'"
- A strand of hair = One single hair
- Strands of hair = two or more, it does not specify
Note that we do not say "Strands of Hairs."
Thanks Maulik.V and Snailboat.
Best Answer
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