問題詳情：
Earth Day， 4 （mark）on 22 April，is an annual event aiming to raise public awareness about environmental protection. First celebrated 5 1970，the Day now includes events in more than 190 countries and regions（地區）. No matter what you like to do，there is a way to get involved in various 6 （activity） on Earth Day. You can plant a tree，make a meal with locally grown vegetables，or save power—the possibilities are endless.
【回答】
4. marked 5. in 6. activities
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