Carl Sagan's famous sayings are as follows: 1. Our cognitive ability is deceptive. Sometimes we see things that don't actually exist. We have to suffer from visual illusions. Occasionally we have hallucinations. We make mistakes easily.

2. In our time, it is technically no problem to completely forge real still life, moving pictures and audio tapes. In our era, every family has a TV set, and the critical thinking ability is declining day by day. It seems possible to fabricate new social memories again, even without the excessive attention of the secret police.

3. Except hydrogen, all the atoms that make up each of us-iron in our blood, calcium in our bones and carbon in our brain-are made by the huge red planet several light years away and billions of years ago.

4. Science has made unprecedented great energy come true, which requires that the whole body of science should pay unprecedented attention to morality, and the importance of science and democracy should also be fully reflected in public education.

5. We are all stardust. At this moment, you are alive. This is a remarkable thing. You live on this planet, breathing air, drinking water and enjoying the warmth of the nearest star.