Silk ________ in _______ China.
-- Did you visit your grandparents yesterday?--Yes, and when I got there, they _____ in the fields .
_____ is known to all is that effective measures should be taken to deal with the problem of the over-exploiting of our resources.
In Australia, surfing is a popular sport among young people _____ they can seek excitement and adventure.
The children went home from the grammar school, their lessons _____ for the day.
Cheating is strictly forbidden in this important exam, and students ______ bring any reference books into their classrooms, cell phones included.