(2012·山东) After completing and signing it, please return the form to us in the envelope __________.
Because the youth can’t____the temptation of surfing the Internet, we should take proper measures to stop it.
There is no known_____for this disease but it can be______.
Green plants breathe_____oxygen in sunlight.
He’s only 17 and____not eligible to vote.
These children are polite and never speak loudly in class. _____.