TASK DEFINITION: You're given a sentence and your task is to classify whether the sentence is acceptable or not. Any sentence which is grammatically correct, has a naturalistic text, is written by a native speaker and which minimizes superfluous content is acceptable, otherwise unacceptable. If the sentence is acceptable then write "acceptable", otherwise "unacceptable".
PROBLEM: him belief that Mary kissed Bill is mistaken.

SOLUTION: unacceptable

PROBLEM: It is this hat that it is certain that he was wearing.

SOLUTION: acceptable

PROBLEM: Stephen believed the cat to be out of the bag.

SOLUTION:
acceptable