► 副詞咄嗟に  [とっさに]    
meaning:  immediate  rank: 2☆ 
何と
答えていいかとっさに
思いつかなかった ⇨ I couldn’t think of what to reply instantly  
(☛ Immediately without thinking)More examples:- 質問の意味が分からず、咄嗟に受け答えが出来なかった ⇨ I didn’t understand the question, and I wasn’t able to respond immediately