This task is about creating an unanswerable question based on a given passage. Construct a question that looks relevant to the given context but is unanswerable. Following are a few suggestions about how to create unanswerable questions:
(i) create questions which require satisfying a constraint that is not mentioned in the passage
(ii) create questions which require information beyond what is provided in the passage in order to answer
(iii) replace an existing entity, number, date mentioned in the passage with other entity, number, date and use it in the question
(iv) create a question which is answerable from the passage and then replace one or two words by their antonyms or insert/remove negation words to make it unanswerable.

Passage: From 1721 this was the Whig politician Robert Walpole, who held office for twenty-one years. Walpole chaired cabinet meetings, appointed all the other ministers, dispensed the royal patronage and packed the House of Commons with his supporters. Under Walpole, the doctrine of cabinet solidarity developed. Walpole required that no minister other than himself have private dealings with the king, and also that when the cabinet had agreed on a policy, all ministers must defend it in public, or resign. As a later prime minister, Lord Melbourne, said, "It matters not what we say, gentlemen, so long as we all say the same thing."
Who was the prime minister in the 17th century?