People have always been curious ______ how living things on the earth exactly began.
―I’m too tired. I want to give up.― If you don’t ________, you’ll win in the end.
---What did the Englishman say?---Oh, he asked where ____ .
The number of the students in our school ____ rising since 2006.
Helen has had a lot of trouble these days,but she doesn’t know whom to ______ for help.
I have been teaching for over twenty years, but never _____ a girl as bright as Lily.