--- Betty , welcome to my birthday party . Please make yourself at home . --- ________.
David worked hard at his lessons ____ he gained high grades in the exams.
As a young man, Zhou Enlai ____ the students movements and later ____ the Communist Party of China.
Camels were ____ better than horses for travelling a long distance.
When I was in the countryside, I ____ by the riverside every day.
The book has been translated into thirty laguages since it ____ on the market in 1973.