EXPLANATION

Thesis "a" may not be researchable, since you'd need to find primary sources to really prove Shakespeare's intent (letters or diaries or notes for plays that Shakespeare wrote). Although you could provide evidence from the play itself to show that Shakespeare intended the audience to question the existence of the ghost, there's other evidence in the play that contradicts this stance. Therefore, you'd need the more "irrefutable" type of evidence that a primary source would provide in this case.