After reading this discussion: is-there-a-correct-gender-neutral-singular-pronoun-his-vs-her-vs-their, I was wondering if I could use one and singular they together in a sentence.
A sentence for an example:
Quite frankly, one needs to get their head screwed on right.
Is that sentence above acceptable grammatically? I also wonder whether I need the pular form of head i.e. heads after their.