1) The Amazon rainforest produces more than 20% of the world's oxygen.

2) The word "umbrella" contains three vowels: U, E, and A.

3) Democracy is a system of government in which power is vested in the people, who exercise it through elected representatives. It allows for political participation, freedom of speech, and protection of individual rights and liberties.

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