instruction: Is the next sentence syntactically and semantically acceptable?

Alex read the newspaper in an hour.

response: acceptable

instruction: Is the next sentence syntactically and semantically acceptable?

They would have been walking for hours.

response: acceptable

instruction: Is the next sentence syntactically and semantically acceptable?

What this girl in the red coat will do is put a picture of Bill on your desk before tomorrow.

response: acceptable

instruction: Is the next sentence syntactically and semantically acceptable?

The knife that he threw into the sea had a gold handle.

response:
acceptable