・It is imperative that we (should) act at once.＝It is imperative for [《米口語》 on] us to act at once. すぐ行動す

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・It is imperative that we (should) act at once.＝It is imperative for [《米口語》 on] us to act at once. すぐ行動す🔗⭐🔉

・It is imperative that we (should) act at once.＝It is imperative for [《米口語》 on] us to act at once. すぐ行動することが絶対必要だ.

研究社新英和大辞典ページ 197338 での【should】単語。