— Are these your English books?— Yes, ________.
In those days, books could only be produced one at a time by hand. __________, they were expensive and rare.
It is clever ________ you ________ me work out the maths problem.
There is ________ in the classroom, so we can see ________.
We should prevent the children ________ the bad programmes.
The Olympics ________ every four years. And the 29th Olympics ________ in Beijing in 2008.