Liu Xi's father kept on____although he was tired.
-- _______ is the man in the white shirt? -- He is an engineer.
In our library, the number of books ________ more than 40,000.
The entrance exam is only fifteen days away from now. You will fail the exam ______ you study hard from now on.
Jack found ______ hard to get along with the other boys in his class.
I have _______ to tell you. Please listen to me.