Answer:
B. Are the characters fully developed?
Explanation:
Making revisions as a writer has to do effecting some changes to the writeup or story to make it more organized, readable and better styled to suit readers.
When a writer is making general revisions, he has to have his characters in mind to know if they are fully developed before making his general revision.
Options A, C and D are questions he has to ask when doing revisions, but checking if this characters are fully developed is done when he's doing a general revision.