1. (2020·哈尔滨模拟) Nowadays, travelling by plane is becoming more and more common. It should be known to you that ___________ for the first time to go by plane.

①you should wear the safety belt well

②you sit on any seat if it is available

③you can eat something to make your ears comfortable

④if you're tired, you can take a walk in the plane

⑤you should never keep an empty stomach to take a plane