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

2) The Amazon Rainforest, located in South America, is the largest tropical rainforest in the world, covering an area of approximately 5.5 million square kilometers (2.1 million square miles). It is known for its exceptional biodiversity and plays a crucial role in the global ecosystem.

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

4) The world's first stock exchange was established in Amsterdam in 1602.