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".

[EX Q]: It is this hat that it is certain that he was wearing.
[EX A]: acceptable

[EX Q]: Susan will never sing at weddings.
[EX A]: acceptable

[EX Q]: Could they have left?
[EX A]:
acceptable