We know _____America is great not because it is perfect but because it can always be made better and _____ the unfinished work of perfecting the union falls to each of its citizens.
The children are giving their classroom a good cleaning, ___ are sweeping; ___ are mopping.
Tom,Bob and Betty have arrived, but ___ students haven’t yet.
He has three pencils.____ is red, ___is blue, and ____ is green.
.She has three brothers.___ is a doctor, ___ are PLA men.
I have two bicycles, ____ is made in Guangzhou;____ is made in Shanghai.