1. (2021·南岗模拟) When we are walking on the street, we need to be careful because there may be some unexpected cases making us in danger, for example, ___________________.

①some drivers drive behind us without making any noise

②something falls from a high building when we are walking

③a car runs across the street fast even though the traffic lights are red

④everyone waits for the traffic lights to turn green before crossing the street

⑤many people are waiting for the bus at the bus stop