He commanded the students _____ the classroom before he returned.
There are some police cars in front. What do you suppose _____?
Tina _____ have known the truth, or she would have told us.
_____ their real economic situations, they got some relief fund from the government.
No matter how frequently _____ the works of Beethoven always attract a large number of people.
The great use of school education is not so much to teach you things _____ to teach you the art of learning.