_________ difficult the task may be, we must finish it on time, because we can’t meet such a precious opportunity _______ we have expected.

There are some warnings in some countries ______ over exploitation of underground water has caused the decline of wetland and increase of desertification.

It was 5 o’clock __________ the visitors finally arrived at Pudong International Airport.

 He bought some books, ______ were expensive.

________ that they lost the game, tears came down Kate's face.