From User Stories Applied book (Mike Cohn), he talked about a "Good user story" which should have these characteristics:
I.N.V.E.S.T (Independent, Negotiable, Valuable, Estimable, Small, Testable)
Your question falls to "Independent" characteristic. The reason to combine OR separate is depending on how to make them "independent".
The reason to split/separate story cards
- The story is bigger than one sprint
- story combine with high and low priority sub stories
The reason to combine story card
- When we see they have "dependency". And after combining, it's not gonna take more than 5 days to implement.
- After combining and it would take more than 5 days, you should find another way to split the story.
About your example:
- I want to post multiple choice questions.
- I want to post true/false questions.
- show a conformation box before clicking the add button
In my opinion, I will leave them as 3 stories because they look independent. Even for "confirmation box", you can implement just a box with add button that can show alert box for confirmation without any questions. Three of them look valuable and independent by themselves. Anyway, Product Owner or Customer is the one who can tell you if the stories are valuable for them or not. So, after splitting or combining, you have to confirm with Product Owner to make sure the stories are still correct.