— Is it convenient if I call you up at 9 tomorrow morning?— I am afraid not. I _____ a group of visiting teachers then.
27. She locked her room _____ a thief would break into it.
26. She said she would spend her holiday ___ Beijing.
25. Whenever I go to Beijing, ____ is quite frequent, I will go to visit the Great Wall.
22. The two boys fought and fought until one ______.
He will _____ our class to sing at the school singing contest.