It was in the mid-1980s that cartoons began to take off in China,_________there were only pictured-story books.
______ chemistry is a branch of chemistry.
More and more high-rise buildings have been built in big cities ______ space.
---We haven’t seen each other for ages.---No, I don’t remember how many years ago _______ I last saw you.
We are still at the airport.If it weren’t for the delayed flight, we _______ the concert right now.
_____ his research paper, Professor Reagan experienced various hardships and loneliness for nearly half a year.