It was not until she got home __ Mary realized she had left her books in the classroom.
---- Putting on a happy face not only helps us make friends but also makes us feel better. ---- _______.
The Human Development Report shows that we are making progress in many different aspects but ______we need to make great efforts.
Coal was formed out of dead forests through a long _____ of chemical changes.
The reason _____ the president of Czech is widely discussed recently is _______ he was seen “to steal” a pen at a press conference in Chile.
The expert warns the Internet users not to ______ their personal information to strangers.