—Can I join the club, Dad?—You can when you _____ a bit older.

 It was the third time that I ________ of the changes of the timetable.

—What’s that noise, John?—Oh, don’t you know that the school library      ?

John kept looking at the pretty girl, wondering whether he_________ her somewhere.

---Why didn’t you go to yesterday’s meeting?---I would have but I ______ too busy working on the important experiment.