--Have you heard of Earth Day ?----Yes . The first Earth Day in 1970 to educate us to

问题补充：

----- Have you heard of Earth Day ?

----Yes . The first Earth Day in 1970 to educate us to protect our planet .

A. celebrates

B. celebrated

C. is celebrated

D. was celebrated

答案：

A. celebrates

B. celebrated

C. is celebrated

(答案→)D. was celebrated

解析：根据语境可知此句的含义是第一个地球日是在1970年举行的。考查的是被动语态的基本构成，因描述的是过去时故用一般过去时的被动语态，其基本构成就是was或were+动词的过去分词，主语是单数故用was，而celebrate的过去分词是celebrated故选D。