They kept trying _________ they must have known it was hopeless

Look at the sign! It says: You______ park your cars here.

John opened the door. There _____ he had never seen before.[ ]

How do you like the movie? — ______, it’s not exciting enough, though lots of money has been spent on it.

I hear that Hu Jintao willcome to Nantong because the Sutong Bridge is open to traffic soon.— Do you know _______