■ hair

通常是不可数名词，只用单数。

• His hair is black.他的头发是黑色的。

但是也可以作为可数名词指一根根的头发。

• So why has he got two blonde hairs on his jacket?那么为什么他外套上有两根金色头发呢？

• obligation 与 duty
• obscene
• occupy
• occur
• of
• of
• of a
• of all
• off
• offend
• offer
• office
• off of
• of itself
• of one's
• often
• oil
• old
• on
• on
• on a first-name basis
• once
• one
• one
• one in