upon是什么意思？

Moreover, students should be prepared not just for their first job, but for their 4th and 5th jobs, as there's little reason to doubt that people entering the workforce today will be called upon to play many different roles over the course of their careers.

The ability to draw upon every available tool and insight—picked up from science, arts, and technology—to solve the problems of the future, and take advantage of the opportunities that present themselves, will be helpful to them and the United States

White students tend to look down upon their black peers.

Many people now tend to look down upon working with hands.

Young people no longer look upon skill as an important asset

How did Erin White feel upon seeing Barack Obama's victory in the election?