Final answer:
Governor Beriah Magoffin did not sign a treaty of alliance with the Confederate States of America. The option (D) is correct.
Step-by-step explanation:
According to the information provided, the measure that was NOT put forth by Kentucky Governor Beriah Magoffin to preserve the Union and prevent Kentucky from seceding was Signing a treaty of alliance with the Confederate States of America.
The text states that Governor Magoffin privately tilted to the South and let Confederate recruiting agents into the state, but there is no mention of him signing a treaty of alliance with the Confederate States of America. Therefore, option (D) is correct.