You will be given a definition of a task first, then some input of the task.
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: The lyrics of the modern Japanese national anthem, Kimi ga Yo, were written in the Heian period, as was The Tale of Genji by Murasaki Shikibu, one of the first novels ever written. Murasaki Shikibu's contemporary and rival Sei Shonagon's revealing observations and musings as an attendant in the Empress' court were recorded collectively as The Pillow Book in the 990s, which revealed the quotidian capital lifestyle. The Heian period produced a flowering of poetry including works of Ariwara no Narihira, Ono no Komachi, Izumi Shikibu, Murasaki Shikibu, Saigyo and Fujiwara no Teika. The famous Japanese poem known as the Iroha (), of uncertain authorship, was also written during the Heian period.
Output:
When were the lyrics of the ancient japanese anthem written.