Singular they = general they Well, here is the situation. I have four students. They did a test. Suppose that the regulation is a student getting a score below 40 gets the remark "study hard" which is written at the bottom of the work instead of a numerical score. When I want to confirm this, may I say:  They get study hard if their SCORE IS (instead of SCORES ARE) below 40, right?
"On their back" or "on their backs"? After the therapy, eight children (43%) became able to crawl/move on their back.   Or should I use "on their backs"?   Singular because each child only has one back, or plural because we're dealing with eight backs?
Is it correct to say "I write children books" (not possessive case)? Although Children's books is what everybody says, I would like to understand why the genitive case is applied in such case.  If I write books for children, children is an adjective here; not the owners of my book! The word "children" just defines or characterizes the type of books I write. Therefore, it's an adjective.   So, I understand that genitive/possessive case ("I write children's book")  is incorrect grammar.  My question is: is the genitive case here really accepted as right? If I use "I write children books" (following the grammar principle) as as I say "I write pets books" (books about pets, and not possessions of pets) - would I be incorrect? Why?