I believe that the 21st century is one ______ China will become one of the most powerful economic countries.
They want to make _______ clear to the public that they are doing an important and necessary job.
_____ the child to bed, she began to correct the pupil’s exercise.
____ with a difficult situation, Arnold decided to ask his boss for advice.
It was ______ back home after the experiment.
It was 1969___ the American astronauts succeeded in landing on the moon.