阅读短文，回答问题。 On March 27, Saturday evening, people all over the world once again turned their lights off for an hour to help fight against global climate changes and give the world a brighter future. For Earth Hour 2010, many best-known buildings went dark from 8:30 to 9: 30 local time, such as the Eiffel Tower, Big Ben, Sydney's Opera House and Beijing's Forbidden City, etc. Millions of businesses and homes around the world also turned off their lights. Some 4, 000 cities in more than 120 countries volunteered to turn off Saturday to reduce energy consumption (能量消耗). 'We have everyone from Casablanca to the camps of Namibia and Tanzania taking part,' said Greg Bourne, CEO of WWF (World Wildlife Fund) in Australia, which started Earth Hour. Earth Hour began in Sydney, Australia, in 2007. In 2008, the event turned into an international one, which has drawn the participation of hundreds of towns and cities worldwide. Now in its fourth year, more and more cities from the world took part in Earth Hour as a show of support for action against global warming. In a WWF survey after Earth Hour 2009, 80 million U.S. citizens said they had participated, according to Ann. 'Earth Hour has always been an event about families and individuals as well,' Ann said, 'and it's really about Americans and people all over the world standing up and saying climate change is real and we need to do something about it now.' However, Earth Hour's energy-saving influence is limited. But WWF says that Earth Hour's real value is symbolic (象征的). 1. Did people all over the world turn off the lights on March 27? ________________________________________________________________ 2. What time did the best-known buildings go dark? ________________________________________________________________ 3. Where did Earth Hour start in 2007? ________________________________________________________________ 4. How many times have we had this event since 2007? ________________________________________________________________ 5. What is the passage mainly about? ________________________________________________________________