2-C. Researchers will no doubt continue to come up with more ideas to enhance the quality of our waiting time.Researchers will no doubt continue to come up with more ideas to enhance the quality of our waiting time.
5-C. (Man:) Well, I doubt she'll accept it. It's too recent.(Man:) Well, I doubt she'll accept it. It's too recent.
(男:)まあ、私は疑います、彼女がそれを受け入れるかどうかダヨ。それはあまりにも最近です。
6. There is no doubt that the resultant sense of crisis drove Japan forward to achieve modernization.There is no doubt that the resultant sense of crisis drove Japan forward to achieve modernization.