Many people believe we are heading for environmental disaster _____we radically(彻底地) change the way we live.
Speaking of all the songs he has written, I think this is probably his _______ one.
The medicine works more effectively _______ you drink some hot water after taking it.
--- Bob, you are absent-minded! --- Oh, I’m sorry I _______ attention to you, Miss Shute.
There was a teapot shaped like a duck, out of _______ open mouth the tea was supposed to come.
--- Mrs. Smith, please teach me how to draw on the computer today. --- Oh, no._______. You have to get familiar with the keyboard first.