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 Gregorian calendar is a solar calendar. A regular Gregorian year consists of 365 days, but as in the Julian calendar, in a leap year, a leap day is added to February. In the Julian calendar a leap year occurs every 4 years, but the Gregorian calendar omits 3 leap days every 400 years. In the Julian calendar, this leap day was inserted by doubling 24 February, and the Gregorian reform did not change the date of the leap day. In the modern period, it has become customary to number the days from the beginning of the month, and February 29th is often considered as the leap day. Some churches, notably the Roman Catholic Church, delay February festivals after the 23rd by one day in leap years.
What calendar is a lunar calendar?

Passage: When Yesün Temür died in Shangdu in 1328, Tugh Temür was recalled to Khanbaliq by the Qipchaq commander El Temür. He was installed as the emperor (Emperor Wenzong) in Khanbaliq, while Yesün Temür's son Ragibagh succeeded to the throne in Shangdu with the support of Yesün Temür's favorite retainer Dawlat Shah. Gaining support from princes and officers in Northern China and some other parts of the dynasty, Khanbaliq-based Tugh Temür eventually won the civil war against Ragibagh known as the War of the Two Capitals. Afterwards, Tugh Temür abdicated in favour of his brother Kusala, who was backed by Chagatai Khan Eljigidey, and announced Khanbaliq's intent to welcome him. However, Kusala suddenly died only four days after a banquet with Tugh Temür. He was supposedly killed with poison by El Temür, and Tugh Temür then remounted the throne. Tugh Temür also managed to send delegates to the western Mongol khanates such as Golden Horde and Ilkhanate to be accepted as the suzerain of Mongol world. However, he was mainly a puppet of the powerful official El Temür during his latter three-year reign. El Temür purged pro-Kusala officials and brought power to warlords, whose despotic rule clearly marked the decline of the dynasty.
How did Yesun Temur die

Passage: San Diego hosts several major producers of wireless cellular technology. Qualcomm was founded and is headquartered in San Diego, and is one of the largest private-sector employers in San Diego. Other wireless industry manufacturers headquartered here include Nokia, LG Electronics, Kyocera International., Cricket Communications and Novatel Wireless. The largest software company in San Diego is security software company Websense Inc. San Diego also has the U.S. headquarters for the Slovakian security company ESET. San Diego has been designated as an iHub Innovation Center for collaboration potentially between wireless and life sciences.

Why is San Francisco known as an iHub Innovation Center?