题目

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 12th. Li Li and Lin Tao are digging on a hill nor 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 5th was named as Tree Planting Day.Then, in 1979, the day_______to March 12th, to _______the date on which Sun Zhon15、正数的任何次幂都是 正数，负数的 奇次幂是负数，负数的 偶次幂是正数．