Which of the following tasks did China work on to improve the air quality before the 2008 Summer Olympics?

A. Replacing polluting taxi cabs

B. Replacing coal furnaces

C. Building new subway lines

D. All of the above

D. All of the above

Along with new railways, airports and roadways, the whole nation’s plumbing system was reworked as part of the preparations for the Games. Entire river systems were altered with water, sewage and industrial wastewater pollution standards substantially upgraded. Ten years ago, finding a relatively clean western-style toilet complete with paper was a treat to find.

Some 300,000 high-polluting vehicles have been banned during the games. Gridlock was relieved by imposing alternate-day driving rules - even number plates on one day, and odd number plates the next - effectively halving the 3.3m vehicles on the road.

Major construction works were also halted and more than 100 factories in Beijing and 56 power plants, many of them coal-fired, were shut down for the duration of the games.