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".

[Q]: I know which guys you've dated, but I don't know which guys you haven't.
[A]: acceptable


[Q]: Willy is taller than that Bill is is generally believed.
[A]: unacceptable


[Q]: An echoing voice rang out.
[A]:
unacceptable