The chairman thought _____ necessary to invite Professor Smith to speak at the meeting.
The ____________ shoes were covered with mud, so I asked them to take them off before they got into __________ car.
In our class, when the bell rang and the teacher closed his book, it was a ______ for everyone to stand up.
Hiking by oneself can be fun and good for health. It may also be good for ______ building.
China has got a good for fighting against the flu with its careful and smooth organization.
To save some of the human languages before they are forgotten, the students in our school started a discussion “Save Our ________”