—How do you plan to travel to Beijing, Jack?—I haven’t made up my mind ________to go by plane or not.
It’s a lovely day, _________?
She hasn’t visited Thailand _______ England yet.
–How long has Mr. Liu taught English? --- _______ 1998.
–Would you like to go to see the film with us? --Sorry, I can’t. Because I ________ it twice.
Scientists think that there has been life on Earth for _______ years.