They        have arrived at lunchtime but their flight was delayed.

---“Why do you have to be there at six?”---“The teacher demands that everyone _____in his seat at six.”

—The research on the new bird flu virus vaccine is challenging and demanding. Who do you think can do the job?—____ my students have a try?

 It was playing computer games that cost the boy plenty of time he ____ doing his lessons.

But for the metal cage to pull the miners to safety, the miners in Chile ____ in less than twenty-four hours.