instruction: Is the next sentence syntactically and semantically acceptable?

My brother is an Einstein at maths.

response: acceptable

instruction: Is the next sentence syntactically and semantically acceptable?

Shelly loves who?

response: acceptable

instruction: Is the next sentence syntactically and semantically acceptable?

The man I think that chased Fido returned.

response: unacceptable

instruction: Is the next sentence syntactically and semantically acceptable?

My heart is pounding.

response:
acceptable