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) Rihanna, born Robyn Rihanna Fenty, is a Barbadian singer, actress, and businesswoman. She has achieved great success in the music industry with hits like "Umbrella," "Diamonds," and "Work," and has also ventured into the worlds of fashion and cosmetics with her brands.

3) The fastest land animal is the cheetah, capable of reaching speeds up to 70 miles per hour (113 kilometers per hour) in short bursts.

4) The word "yesterday" contains three vowels: E, A, and A.