What ___ wonderful time we had yesterday!
You must watch carefully everything _____ the teacher does in class.
She didn't come to his birthday party just_____ what he had said to her the day before.
Drivers are warned that it is dangerous to talk on the phone while________.
The Great Wall is _________________ tourist attraction that millions of people pour in every year.
They began to consider what use could ___ the natural resources(资源).