--__is that on the desk? --My Chinese book.
If there are ______ trees, the air in our city will be _______ cleaner.
You shouldn't ____ the boy's mistakes.
______our teacher is ill, ______ he still comes to our class to teach us.
The teacher said that the earth ______ around the sun.
I felt it hard to keep up with my classmates. But whenever I want to__ __,my teacher always encourages me to work harder.