try to understand ________ that prevents so many children from being happy, there seem to be three causes.

g a diary is ____ good habit, by which you’llmake ____ great progress in writing.

________trees we plant，________our city will be．

How does your second-hand car run? —- It _____ run all right, but it is being repaired

Li Fan won the first prize in the national physics competition. — I ________ he was the winner.