One crucial variable Beijing's organisers cannot control is the city's air pollution problem.
An IOC inspection team visited the Chinese capital and admitted smog was a concern, despite assurances that traffic controls and factory shutdowns would improve air quality.
Olympics chief Jacques Rogge said: "If the atmospheric pollution is too high at certain times then we might consider rescheduling."
One pilot scheme to reduce emissions saw cars with registration plates ending in odd numbers banned for one day, with even numbers banned the next.
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