A hard-working man ______ become a great scientist, but a great scientist _______ be a hard-working man.
They are _______ little sheep that we can’t make much money by selling _______.
---Do you know how long ________? ----I’m sorry I don’t know.
Jim has many hobbies, ________ swimming, hiking and playing badminton.
I _____ the book for two weeks. I must return it to the school library.
Though it was very late, they _______their discussion.