When you feel you are happier and more relaxed after having a cigarette, you may become ________addicted.

He has called several times this morning; _____ there is something very important.

As is known to all language learners, newly learnt words will soon be forgotten unless ______ used in everyday communication.

--___do you clean the reading room? ---Every two or three days.

While typing, Helen has a habit of stopping _____ to give her long and flowing hair a smooth.