To add a quiz correctly, it needs an association of at least one subject or School.
First, add a subject, for example, "English", type a comma,
or hit "enter" to insert the first subject, feel free if you want to add multiple ones.
The other required field is the School, you should also add at least one School, type the name of
the School, for example, "Diamond Academy", type a comma, or hit "enter" to insert it.
To delete an element, such as a subject, hover over the subject and click on the cross mark.
To update the name of an element, click on it, change its name, and save.
Now you have access to the list of subjects and schools when you try to add a quiz, for example,
we'll create a new quiz, using the subject "English" and the school "Diamond Academy".
If you return to the settings, "quiz custom fields"
and try to remove "English", it'll show you a warning,
which explains that you can't delete a subject if already it's assigned to a quiz.
Same for the School.
To remove an assigned subject, you should first go to the quiz using this subject,
go to "Edit", then click on the gear icon related to the settings,
Assign the quiz to another subject, for example, "German", save the changes.
Now, if we return to Quiz Custom fields again,
and try to remove English; it will be removed because it's not associated anymore with any quiz.
