The right answer is Russia.
The Kingdom of Poland was given to the Tsar, after the Congress of Viena in 1815. Alexander I decided to give a liberal constitution of its own to that new state and became King of Poland himself. Polish administration, Polish Diet (parliament), and army were maintained. He also promised to reunite with the Kingdom those former Polish provinces that had been annexed by Russia during the partitions, but it was never to be done. In this way, the liberal, constitutional Kingdom of Poland became an autonomous part of the despotic Russian Empire.