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: He has seen his children.

SOLUTION: acceptable

PROBLEM: Bill understands Mary and himself.

SOLUTION: unacceptable

PROBLEM: John is taller than six feet is.

SOLUTION:
unacceptable