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

—Credit cards are       useful when traveling.—True. They save us the trouble of taking too much cash.

At the crossroads, you have to drive very ________ to avoid traffic accidents.

Joe worked so hard that ________ he made himself ill.

I have $50, but that isn’t ____ enough for my journey fare.