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: Tibet retained nominal power over religious and regional political affairs, while the Mongols managed a structural and administrative rule over the region, reinforced by the rare military intervention. This existed as a "diarchic structure" under the Yuan emperor, with power primarily in favor of the Mongols. Mongolian prince Khuden gained temporal power in Tibet in the 1240s and sponsored Sakya Pandita, whose seat became the capital of Tibet. Drogon Chogyal Phagpa, Sakya Pandita's nephew became Imperial Preceptor of Kublai Khan, founder of the Yuan dynasty.
What did the Mongols retain nominal power over?