阅读下面材料，在空白处填入适当的内容（1个单词）或括号内单词的正确形式。

Earth Day 【小题1】 (found) in 1970 as a day of education about environmental problems, and Earth Day 2020 occurs on Wednesday, April 22 — the holiday's 50th anniversary. The holiday is now a global 【小题2】 (celebrate) that's sometimes extended into Earth Week, a full seven days of 【小题3】 (event) focused on green living.

【小题4】 (elect) to the U.S. Senate (参议院) in 1962, Senator Gaylord Nelson was determined to convince the federal government that the planet was 【小题5】 risk. In 1969, Nelson developed the idea for Earth Day after 【小题6】 (inspire) by the anti-Vietnam War "teach-ins" that were taking place on college campuses around the United States.

Denis Hayes, a young activist 【小题7】 had served as student president at Stanford University, was selected as Earth Day’s national coordinator (协调者), and he worked with 【小题8】 army of student volunteers and several staff members from Nelson's Senate office 【小题9】 (organize) the project.

The first Earth Day was effective at raising awareness about environmental problems and transforming public attitudes. Earth Day kicked off the "Environmental decade with a bang," as Senator Nelson later put it. The theme of Earth Day 2020 is "climate action." Earth Day. org hopes it will be the 【小题10】 (large) volunteer event in history.