We are at your service. Don’t ________ to turn to us if you have any further problems.
My friend Tom stays at Internet bars above 8 hours every day ______, really a netter(网虫).
I have many friends, _____ some are businessman.
____ is certain, though, is that the mystery of Tutankhamun’s tomb has never been fully explained.
Some time after the rockets and the space shuttle are _____, the rocket will _____ the space shuttle and ____ the sea.
London people always take umbrellas with them, just _______ it rains.