China has a history of over 5,000 years. It is one of the ________ countries in the world.( )
biggest
richest
oldest
The mobile phone has changed people’s life a lot ________ it was invented.
Getting enough sleep is good for _______ health _______ study.
— Hey, boy. You can’t cross the street now. You have to wait _______ the traffic lights turn green. — Oh, sorry and thank you.
Mom was cooking ________ Dad was reading newspapers.
It’s late. David washes his face _______ goes to bed.