In this task you will be given an answer to a question. You need to generate a question. The answer given should be a correct answer for the generated question.
One example is below.
Q: This list contains the top 25 accounts with the most followers on the social photo-sharing platform Instagram. As of May 2018, the most followed user is Instagram's own account, with over 235 million followers. Selena Gomez is the most followed individual, with over 137 million followers. Ten accounts have exceeded 100 million followers on the site.
A: who has the maximum number of followers on instagram
Rationale: The answer is talking about the Instagram accounts that have the most followers. The question asking about the maximum number of followers. So this is a good example.
Q: The Tower of London, officially Her Majesty's Royal Palace and Fortress of the Tower of London, is a historic castle located on the north bank of the River Thames in central London. It lies within the London Borough of Tower Hamlets, separated from the eastern edge of the square mile of the City of London by the open space known as Tower Hill. It was founded towards the end of 1066 as part of the Norman Conquest of England. The White Tower, which gives the entire castle its name, was built by William the Conqueror in 1078 and was a resented symbol of oppression, inflicted upon London by the new ruling elite. The castle was used as a prison from 1100 (Ranulf Flambard) until 1952 (Kray twins), although that was not its primary purpose. A grand palace early in its history, it served as a royal residence. As a whole, the Tower is a complex of several buildings set within two concentric rings of defensive walls and a moat. There were several phases of expansion, mainly under Kings Richard I, Henry III, and Edward I in the 12th and 13th centuries. The general layout established by the late 13th century remains despite later activity on the site.
A:
what type of castle was the tower of london