These two countries held a commonwealth from the 16th to 18th century.

The story behind the answer

Poland and Lithuania is correct: in 1569 the Union of Lublin formed the Polish-Lithuanian Commonwealth, a dual state with a shared elected monarch, parliament (Sejm), and foreign policy, lasting until its partitions in 1772–1795. It grew into one of Europe’s largest, most diverse realms, known for relative religious tolerance and the nobility’s “Golden Liberty.”

To remember it, think "Lublin links lands": the Union of Lublin linked Poland and Lithuania. The other options don’t fit: Hutu is an ethnic group, not a country; Bangladesh and Bhutan were never united; and the Koreas became separate states only in the 20th century.