1 . “Leave a place better than you found it.” It’s a _________ philosophy, but one that William Lindesay holds dear. On April 22, which was also Earth Day, he led twenty _________ to help clean up the Badaling section of the Great Wall.

He who _________ is the owner, William said in the _________ remarks of the cleanup event in 2000. “The Great Wall _________ China, and is also one of the greatest structures in the world. Everyone has a _________ to protect it. Every day should be Earth Day,” he said.

During the past three decades, he has spent most of his time _________ and exploring the Great Wall and has developed his own efforts to protect the cultural relic.

“It's a _________ thing that people are going out to enjoy themselves and to _________ the great history and heritage, __________ it's also quite dangerous if they don't __________ how fragile the historical sites are and how fragile the __________ is,” William said.

In 1989, his first __________ Alone on the Great Wall was published, and he has published another five books about the Great Wall since then. In 2001, he __________ International Friends of the Great Wall, an association whose efforts are aimed at protecting this __________ to the past.

His next step is to organize exhibitions about the Great Wall as a monument over the last 400 years. The exhibitions are expected to be held in Beijing, London, Paris and Washington D. C