51. They planned to go to Beijing for sightseeing, but because of their daughter’s unexpected illness they had to stay at home _____.
--- How about _________ Christmas evening party? __ I should say it was __________ success.
---Lost and Found office. ________? --- I wonder if you have a small black suitcase of mine.
So far all cloned animals have suffered from some different serious disorders, _______ dying soon after birth.
When asked to explain ________ he does to make his students so fascinated with his lessons, the teacher paused and thought deeply.