1．(2019年北京卷·语法填空)Earth Day, marked on 22 April, is an annual event aiming to raise public awareness about environmental protection.First celebrated ________ 1970, the Day now includes events in more than 190 countries and regions (地区)．
2．(2019年浙江卷·语法填空)But can uniforms help improve school standards? The answer ________ this question is not clear.
3．(2019年天津卷·单项填空)A study shows the students who are engaged in afterschool activities are happier than ________ (that) who are not.
