This task is about reading the given passage and construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) its answer is a continuous text span from the paragraph. Avoid creating questions that (i) can be answered correctly without actually understanding the paragraph and (ii) uses same words or phrases given in the passage.
Q: 
 Great Britain: The torch relay leg held in London, the host city of the 2012 Summer Olympics, on April 6 began at Wembley Stadium, passed through the City of London, and eventually ended at O2 Arena in the eastern part of the city. The 48 km (30 mi) leg took a total of seven and a half hours to complete, and attracted protests by pro-Tibetan independence and pro-Human Rights supporters, prompting changes to the planned route and an unscheduled move onto a bus, which was then briefly halted by protestors. Home Secretary Jacqui Smith has officially complained to Beijing Organising Committee about the conduct of the tracksuit-clad Chinese security guards. The Chinese officials, seen manhandling protesters, were described by both the London Mayor Ken Livingstone and Lord Coe, chairman of the London Olympic Committee as "thugs". A Metropolitan police briefing paper revealed that security for the torch relay cost £750,000 and the participation of the Chinese security team had been agreed in advance, despite the Mayor stating, "We did not know beforehand these thugs were from the security services. Had I known so, we would have said no."
A:
Which city hosted the 2012 Summer Olympics?