②は全てIt … that+S+V~の形式主語構文です。
1. ①Most Japanese <seem> to [be hardworking]. ②It <seems> that most Japanese [are hardworking]. 形式主語構文
2. ①Emily <seemed> to [be happy]. ②It <seemed> that Emily [was happy]. 形式主語構文
3. ①He <is believed> to [be a great musician]. ②It <is believed> that he [is a great musician]. 形式主語構文
4. ①He <was believed> to [be a great musician]. ②It <was believed> that he [was a great musician]. 形式主語構文
参考にしてください。