✨ ベストアンサー ✨
ポイント:否定語(句)+「倒置」(=疑問文の語順)
1. <Never> [have I heard] anything bad about Shinkansen trains. <否定語(句)> [倒置]
2. <Rarely> [have we seen] dust in his room.
3. <Few foreign passengers> [do we see] in the local train.
4. <Only to clean his room> [did he buy] an expensive robot cleaner.
参考にしてください。
ありがとうございました!!