In our class, when the bell rang and the teacher closed his book, it was a ____ for everyone to stand up.
The meeting was _____ when the chairman fell ill.
The members of the club wouldn't run a ____ entrusting(委托) the organization to an unreliable person.
Many new _____ will be opened up in the future for those with a university education.
It isn't quite _____ that he will be present at the meeting.
The island where these rare birds nest has been declared a _____.