I’m terribly sorry to turn you down this time, but I promise I will ______ to you next time.

Chemical processes _______in the treatment of materials for clothes _______the environment badly in some countries nowadays．

With the aid of the scientists, more new facts about the sea will _______ gradually.

---Cliff, I lost your bike at school. I suppose I should pay for it.---Oh, ______. It was an old bike anyway.

Because of the heavy foggy weather, we had to _______ the plan of going to Xi’an for the football game by air.