The government __________ air quality in urban areas from level one to five : excellent,fairly good, slightly polluted, poor and dangerous.
--- It’s wrong of a student to follow ______ his teacher says. --- It’s true. I can’t agree ______.
The teacher set such a difficult problem ________none of us could solve.
If we want ______much cleaner world, we should reduce _______ emission of carbon dioxide.
This morning my mother told me _____ she would attend a wedding party _____ she wouldn’t come back home for lunch.
It is the test system, _____ the teachers, that is to blame for the heavy burden(负担)of middle school students nowadays.