instruction: Is the next sentence syntactically and semantically acceptable?

That piano, the boy's loud playing of which drove everyone crazy, was badly out of tune.

response: acceptable

instruction: Is the next sentence syntactically and semantically acceptable?

There might be a unicorn in the garden.

response: acceptable

instruction: Is the next sentence syntactically and semantically acceptable?

We saw him beaten by the champion.

response: acceptable

instruction: Is the next sentence syntactically and semantically acceptable?

John talked to every woman who came up to him.

response:
acceptable