---Is the Youth Center open to the public yet?---Yes. It ______ for almost one and a half years.
I am very tired because I up late.
You will find you can enjoy so many books if you English.
Don’t come into the lab ________ you are asked to.
My uncle has been taught in this school _______ he was twenty years old.
Don’t worry, sir. I’m sure I can run _____ to catch up with them.