I can't decide whether to postpone or (to) cancel it.
それを延期すべきか取りやめるべきか決めかねている
I can't square it with my conscience.
良心がとがめてそれはできない
I can't take the credit for it.
それを自分の手柄にはできない
I cannot say it anyway.
どうしてもそれが言えない
I couldn't keep from thinking about it.
それを考えないわけにはいかなかった
I couldn't [tried to] think of his name [(of) where I'd heard it].
彼の名前を［それをどこで聞いたか］思い出せなかった［思い出そうとした］
I did it, and so did he.
私がそれをしたら彼もした
I discerned that it was important.
それが重要だと悟った
I don't know about that.
さあそれはどうだか（◆不賛成）
I don't know [am not sure] but it is all true.
たぶんそれは本当なのだろう
