What Do You Mean by Not Greeting Aliens?

"The International Academy of Astronautics has released a document. Please do not reply to aliens without authorization. If you find aliens, please notify the United Nations and local police as soon as possible." "Does anyone know the phone number of the United Nations and are you serious about calling the police? Police: Is it true that I beat aliens?" "An unknown comet is coming tomorrow night. Do you think it could be an alien?" "Tomorrow night might be the end of the world, and I still have 10 yuan in savings that I haven't spent yet!" "I just connected to the Internet, why are the whole Internet saying that tomorrow is the end of the world, the end of the world, etc. I just finished the college entrance examination, and my mother just bought a computer!"