Earth Day is a yearly event celebrated on April 22. Various activities    1    ( hold ) worldwide to show support for environmental protection. Here is a brief history of    2    event.

In the 1960s, Americans were becoming aware of the effects of pollution    3    the environment. In 1969, Senator (参议员) Gaylord Nelson,    4    ( consider )one of the leaders of the modern environmental movement, developed the idea of Earth Day. His idea really raised    5    (aware )about the environment. On April 22, 1970, over 20 million people turned up for the first Earth Day. They believed it was important    6    ( keep ) the planet safe.

In 1990, Earth Day went global, with 200 million people in over 140 nations     7    ( participate ). In 2000, Earth Day focused on clean energy and involved hundreds of millions of people in 184 countries and 5000 environmental    8    ( group ). Activities ranged from a traveling to a gathering of hundreds of thousands of people at the National Mall in Washington, D. C. Today, the holiday is a global celebration    9    is sometimes extended (延长) into Earth Week, a full seven days of events focusing on green living. In 2018, more than 1 billion people were involved in Earth Day activities, making it one of the    10    (large)events in the world.