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

In my view, biology is ______ chemistry, but a little easier than mathematics.

Drunk driving used to occur _______, but now it is under control.  

—Thank god, you finally returned home ________. —You can never imagine how I worried about you when I was told about the terrible accident. 

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