After pains-taking efforts, he eventually concluded that the principle he stuck _______ true.
The students in the university are all taking courses _______ a degree.
One of the best ways for people to keep fit is to _______ healthy eating habits.
I couldn’t _______.The line was busy.
It’s ten years since the scientist _______ on his life’s work of discovering the valuable chemical.
This picture was taken a long time ago.I wonder if you can _______ my father.