You could hardly imagine _____ amazing the Great Wall was _____you saw it with your eyes.
His grandma has_______ for 5 years.
The scientist_______ everyone ______ our environment .
Tim is weak in math, so he is trying _________ up with other students now.
Every student in our calls is looking forward to ______a good future.
I must return the two books to the library. I _____ them for 20 days.