1) The word "oxygen" contains two vowels: O and E.

2) The ancient city of Athens, Greece, is often considered the birthplace of democracy, where citizens had a say in the decision-making process.

3) The Great Wall of China is not visible from space without aid, contrary to popular belief.

4) The concept of quantum computing explores the use of quantum mechanics principles to perform complex computations, potentially revolutionizing fields such as cryptography and optimization.