There are several research centers in China ________ a certain disease called Bird Flu is being studied.
She will have a holiday as soon as she _____ the work next week.
The world _____ . Things never stay the same.
Could you tell me when to get the book _____ I want to read?
The math problem is so hard. I really don’t know _____.
She told us _____ story that we all forget about the time.