Some scientists think that it may take ______years to make robots look like people, and do the same things as us.
When you play sport, you need to guard ______ accidents.
Do you know ______? I want to see a funny film.
The Silk Road was ______ long that it passed through many countries.
When you ______ a difficult task, try to continue with it and finish it.
— There are dark clouds, and the wind is blowing strongly. — It ______ that a typhoon is coming.