If you bump into somebody immediately say excuse me .
你不小心撞到某人，请立即说“对不起”。
The problem is ions that bump into the grid instead of passing through it cause erosion which limits the average nasa ion engine 's lifespan to about 3 years .
Most of us were brought up in a culture of apology : children must say sorry when they do something wrong and grown-ups must apologize if they bump into each other in the street .
Then each bat was instructed to move about on its own on the screen following only a few simple rules encoded into an algorithm : don 't bump into another bat keep up with your neighbors and don 't stray too far away .