根据句意及首字母提示完成句子：

1．Many economists are busy with their r_________ work to solve the economic problems of the world．

2．If you want to learn English well，I think it is very h_________ for you to read it every day．

3．Thank you for the p________ trip to Beijing．We’ll never forget the kind people and nice thing we met．

4．We all should work hard to t_________ our country into a big one．

5．All the students are out on the playground for their PE．The classroom is now e _________．