Duty is an act or a course of action that people ____ you to take by social customs, law or religion.
______ in his studies, he didn't know that all the others had left.
We had much difficulty __________ home in the snowstorm.
“Be careful, do not stand ___________ to the fire, Jim.” Mrs. Thompson said to her little son.
Several pages were found _________ when the book _________ me.
--- How many students are there in your school? --- There are 2,000 students here __________.