1 . It's March 12^th. Li Li and Lin Tao are digging on a hill not far from their school. In China, people across the country plant trees_______on this day.

The idea of planting trees was first put forward in 1911 by Sun Zhongshan, the great_______ in China's history. He said more trees were needed as a_________against flood（洪水）and drought. In 1915, April 5^th was named as Tree Planting Day. Then, in 1979, the day_________to March 12^th, to _______the date on which Sun Zhongshan died.

"Everyone has heard of the Great Wall of China," says Li Li. "But have you heard of the Green Wall of China? That's the biggest tree planting _________ of all. "The Gobi Desert in the north of China was _________every year. So in 1978, a tree planting project was started to _________ Gobi spreading. The government and local farmers have been planting millions of trees to build a great green "wall" along the edge of the desert.

"Tree planting has become a tradition in China now," says Lin Tao. "Almost everyone does it on March 12th. Many people also plant a tree on a _________day. My parents planted a tree when started school. And my cousin planted ________ on his wedding (婚礼) day. We do it for the environment and for ourselves."