1. (2019·烟台) 阅读下面短文，从短文后各题所给的A、B、C和D四个选项中，选出可以填入空白出的最佳选项。

    It's March 12^th. Li Li and Lin Tao are digging on a hill nor far from their school. In China, people across the country plant trees1on this day.

    The idea of planting trees was first put forward in 1911 by Sun Zhongshan, the great2 in China's history. He said more trees were needed as a3against flood(洪水)and drought. In 1915, April 5^th was named as Tree Planting Day. Then, in 1979, the day4to March 12^th, to 5the 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 6 of all. "The Gobi Desert in the north of China was 7every year. So in 1978, a tree planting project was started to 8 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 9 day. My parents planted a tree when started school. And my cousin planted 10 on his wedding (婚礼) day. We do it for the environment and for ourselves."