In 1972, the United Nations hold a meeting in Sweden   _________            
to share ideas about ways to take better care of for the           __________
earth．At the summit, people from more than one hundreds           __________
countries discussed some of the important problems faced           __________
our planet．Since then, several Earth Summits had been held.       __________
In 2002, the Earth Summit was held in Johannesburg.            _________
One of the main theme was “sustainable development”, or     __________
the question what we can continue developing the world         __________
without damage the environment．Most of the speakers           __________
talked the three biggest killers in the world.                     __________