instruction: Is the next sentence syntactically and semantically acceptable?

I will have eaten the beef waffles.

response: acceptable


instruction: Is the next sentence syntactically and semantically acceptable?

They wouldn't leave soon.

response: acceptable


instruction: Is the next sentence syntactically and semantically acceptable?

Stephen is believed to be easy to annoy Ben.

response: unacceptable


instruction: Is the next sentence syntactically and semantically acceptable?

Who bought that piano for his secret fiancée?

response:
acceptable