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: John is taller than Bill.

A: acceptable
****
Q: The box gradually contained the ball.

A: unacceptable
****
Q: Why haven't any books been returned?

A:
acceptable
****