1) The concept of separation of powers, as articulated by French philosopher Montesquieu, refers to the division of government responsibilities into distinct branches, such as the executive, legislative, and judicial, to prevent concentration of power.

2) The concept of 3D printing, also known as additive manufacturing, was first introduced in the 1980s and has since revolutionized prototyping and small-scale production.

3) The word "music" contains two vowels: U and I.

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