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Ifを使った仮定法でifを省略したものは、【疑問文の順番】って覚えとけば大丈夫です。
If Jim had been on the train, he could not have answered his cellphone.
→ Had Jim been on the train 【過去完了の疑問文】
参考までにいくつか例を。
If I were a bird, I could fly to you.
→ Were I a bird, I could fly to you. 【be動詞の疑問文】
If it should rain tomorrow, we would not go out.
→ Should it rain tomorrow, we would not go out. 【助動詞の疑問文】
大体はこれでなんとかなるはずです。
Had been Jimやと思ってました😅😅
ありがとうございます!助かりました☺️☺️