Whenever it is, it is right for a student to ______ the school disciplines.
It's reported that a plane with five people __________ crashed several days ago.
__________ of 5000 visitors came to the exhibition. And __________,the museum got an income (收入)of $10,000.
The book cost me 12 yuan in all, postage __________.
Walking alone in the dark, the boy whistled to __________ his courage.
I don't think the experiment is __________ failure. At least we have gained __________ experience for future success.