Definition: 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.
Input: Passage: The Chronicle provides a mythic tale of Oleg's death. A sorcerer prophesies that the death of the Grand Prince would be associated with a certain horse. Oleg has the horse sequestered, and it later dies. Oleg goes to visit the horse and stands over the carcass, gloating that he had outlived the threat, when a snake strikes him from among the bones, and he soon becomes ill and dies. The Chronicle reports that Prince Igor succeeded Oleg in 913, and after some brief conflicts with the Drevlians and the Pechenegs, a period of peace ensued for over twenty years.
Output:
What known document tells the birth of Oleg?